Does purging RAM actually do anything?

What the button empties

macOS fills otherwise-idle memory with recently read file data. That cache is not memory being used up: the moment an app needs the room, the system drops the cache itself, without being asked and without slowing anything down. A purge just does it early, and the next time those files are wanted they are read from disk again.

So the number on screen improves and the machine does not. If anything it is briefly slower, because everything the cache was holding has to be fetched back.

The same machine, measured three ways

RefreshYourMac reads these from the kernel's own memory statistics rather than estimating them:

• 40.6 MB genuinely spare — pages nothing wants, which a purge would free for real.
• 3.12 GB of file cache — freed by a purge, and read straight back.
• 4.83 GB held by the compressor — which a purge cannot touch at all.

That last line is the one worth keeping. On this Mac the compressor was holding 18.09 GB held in 4.83 GB: real data belonging to running apps, squeezed down about three and a half times. It is why free memory reads so low on a healthy Mac, and no button moves it.

What to watch instead

• Memory pressure, which is what macOS itself acts on. Green means there is no problem to solve, whatever the free-memory figure says.
• Swap activity — pages moving to and from disk right now. A number that is actually zero most of the time, and the one that means something when it is not.
• The compression ratio, which tells you how hard the system is working to keep everything resident.

Does the command exist?

Yes — /usr/sbin/purge ships with macOS, and the cleaners that offer this button are wrapping it. RefreshYourMac does not, and shows you those three numbers where the button would have been, so the refusal is something you can check rather than something you have to believe.