They contain recently browsed web pages, ARM code translated from Intel executables, security data, font information, and much more. And they can cause problems.
cache
It has been one of the oldest problems on Macs, when a document shows with the wrong icon. Why, and how to fix it?
It is easy to browse images and other documents in the QuickLook cache in High Sierra and earlier, but Apple has not blocked this – details here.
The greatest skill in memory is not the remembering, but knowing what to forget – something that macOS is useless at. Why doesn’t it clear out its old crud?
Sometimes cached data are not as concealed or transient as we might wish. Don’t get cached out by them.
It turns out that Steam’s leak of personal data was very large, did contain sensitive personal information, and was the result of a denial of service attack. Has it been reported, though?
A single point of failure which discarded all privacy protection is hardly an example of good design.
The Eclectic Light Company 