Nine Mac cleaning myths that waste your time

Myth 1: Freeing up RAM makes your Mac faster

This is the big one, because it drives a whole category of "memory cleaner" apps. The belief is that a full memory bar is bad and that reclaiming RAM speeds things up. Apple's own documentation says the opposite, in plain words: "When you have free or unused memory, your computer performance does not necessarily improve," and "macOS obtains the best performance by efficiently using and managing all of your computer's memory."

Modern macOS deliberately keeps RAM full of useful things: recently used files cached for speed, and inactive app pages compressed rather than discarded. That is good engineering, not a leak.

Myth 2: Memory cleaner apps help

If freeing RAM does not help, the apps that do it cannot either. Most of them simply run the built-in purge command, which is redundant. Worse, many run continuously in the background and consume their own slice of memory, which can push your real apps into swap, so the "cleaner" produces exactly the lag it claims to fix. Macworld's guidance is blunt: macOS "is capable of managing memory efficiently... so you shouldn't really need a third-party app to do that for you."

Myth 3: Clearing caches speeds up your Mac

Caches exist precisely to make things faster. They are fast local copies of work the system would otherwise redo, from QuickLook thumbnails to rendered fonts. Clearing them does not speed anything up; it forces everything to be rebuilt, so the usual result is a temporary slowdown while the caches repopulate. As Howard Oakley, who documents macOS internals more rigorously than almost anyone, puts it, clearing caches "shouldn't be considered a routine maintenance procedure."

Myth 4: You must run maintenance scripts

For years, Mac tips told you to run the "daily, weekly, monthly" maintenance scripts, and cleaner apps offered a button for it. The original rationale was that these jobs were scheduled with cron and could be skipped if your Mac was asleep at the scheduled time. That rationale stopped being true long ago: once the jobs moved to launchd, a missed run was simply coalesced and executed the next time the Mac woke.

And now the point is entirely moot. The periodic maintenance tooling was removed in macOS 15 Sequoia. Log rolling moved to the logd service, which keeps logs by total size rather than by age. On a current Mac there is no periodic command, no /etc/periodic directory, and nothing for you or a cleaner app to run.

Myth 5: Repairing permissions fixes problems

This one has been dead even longer. "Repair Disk Permissions" was removed from Disk Utility in OS X 10.11 El Capitan, back in 2015. System Integrity Protection now protects system files so their permissions cannot drift, and macOS repairs them automatically during software updates. The feature is not hidden; it is gone, because it is both unnecessary and, under SIP, impossible for system files.

Myth 6: Emptying the Trash frees space right away

You empty the Trash expecting the free-space number to jump, and sometimes it barely moves. This is not a bug and not a lie from your Mac. On an APFS disk with Time Machine enabled, your Mac takes local snapshots on its own drive, and a snapshot taken before you deleted the files keeps their blocks alive until it expires. One documented test found deleted files still occupying about 95 GB because a Time Machine snapshot was retaining them.

These snapshots are "purgeable," meaning macOS can and does remove them when space is needed, but on its own schedule, not the instant you empty the Trash. We wrote a whole piece on this; the short version is that the space is not lost, it is promised to a snapshot.

Myth 7: More free disk space makes a Mac faster

This was true in the hard-drive era, when a full disk meant fragmented files and slow seeks. On the SSDs in every modern Mac, it is mostly a myth. SSDs do not fragment the way spinning disks did; as Oakley notes, if an APFS disk lost performance simply from filling up with metadata changes, "that would be a serious bug in APFS."

There is a real effect, but it is different: when an SSD gets very full, the drive controller has less room for its write cache and garbage collection, and write speeds can drop sharply. A good practical rule of thumb for a boot drive is to keep around 100 GB free, mostly so macOS updates and large installs have room to work, not to chase a speed boost.

Myth 8: You should TRIM, defragment, or optimize your SSD

On the SSDs Apple fits, TRIM is always enabled; you do not switch it on and there is nothing to schedule. Defragmentation is a hard-drive concept that APFS, built for flash with copy-on-write, makes irrelevant. The only sliver of truth is that a third-party internal SSD might need TRIM enabled once with trimforce; for the drive your Mac shipped with, there is nothing to do.

Myth 9: You need a cleaner app to maintain macOS

Apple's official advice on freeing space is entirely built-in and names no third-party tool: store files in iCloud, optimize storage, empty the Trash automatically, and remove apps and files you do not need. And Apple states that the system already does the housekeeping people buy cleaners for: "When space is needed on your Mac, macOS also clears caches and logs that are safe to delete."

This does not make every utility worthless. The genuinely useful category is the one that shows you your disk and lets you decide, rather than silently deleting things. The tools with the best reputations, like DaisyDisk and the open-source treemap viewers, never auto-delete. The reputations to be wary of belong to apps that delete logs and caches the OS is responsible for. Oakley is direct about one case: "If the housekeeping app you use deletes log files... I'd consider that to be malicious," because those logs feed Time Machine diagnostics and security scans.

So what should you actually do?

Far less than the myths suggest, and all of it is transparent:

1. Judge memory by Memory Pressure, not free RAM. Ignore RAM cleaners entirely.
2. Leave caches, maintenance and permissions to macOS. All three are either automatic or gone.
3. To free space, find what is actually large, understand what each item is, and remove only what rebuilds, keeping roughly 100 GB free on your boot drive.
4. Prefer tools that show and explain over tools that auto-delete.

Sources

• Apple — Activity Monitor User Guide (memory pressure colours; free memory does not necessarily improve performance; cached files and swap); Mac User Guide on optimizing storage (macOS clears safe caches and logs); safe mode support article.
• Howard Oakley, The Eclectic Light Company — caching, memory management, free space on APFS, snapshots and purging, and the risks of deleting logs. Current through macOS Tahoe.
• On removals: the periodic maintenance tooling removed in macOS 15 Sequoia; "Repair Disk Permissions" removed in OS X 10.11 El Capitan under System Integrity Protection.
• Macworld on third-party memory apps; reporting on the CleanMyMac notarization and scareware-impersonation landscape.

Where this article paraphrases community consensus (for example on memory-cleaner apps), it is identified as such rather than attributed to a single authority.