Like most posters and readers here, I’ve been using computers for a very long time. One thing that’s always baffled me is people’s obsessions with clearing out caches.

I’m sure that there are some programs that do caches wrong, and never purge anything, so that purging caches is sometimes beneficial. But I question how many people even know what a “cache” is. People seem to think of “cache” as synonymous with “cruft,” as if it’s garbage that builds up and needs to be manually scraped off of your computer every few weeks so it doesn’t come to a grinding halt.

In actuality, caches help keep your computer running fast, by, well, caching often-used data so that it’s faster to access next time. Your web browser’s cache? That’s so that, next time you load a page, it won’t waste its time downloading content that hasn’t changed. The Windows Prefetch cache? That’s so programs load faster. The thumbnails cache? That’s so that Windows doesn’t have to manually process every 10-megapixel image, in a folder of hundreds, every time you open it.

There are some good reasons to purge your caches, like if you’re dangerously low on disk space. As my previous post indicated, every now and then, something will screw up the concept of “caching” and never remove outdated things from the cache. This is a bug, though, not how most caches work. Most things use either time-based caches (where anything that’s been in the cache for more than, say, a week, will get purged automatically), or size-based caches (where, when the cache reaches, say, 500MB, it will start removing the least-recently-used items). Thus caches shouldn’t be something you need to worry about much.

Another reason to clear out your caches would be if you’re getting weird behavior. This can range from the simply, “Why is Youtube loading in Swedish?” (It somehow got the wrong location data for you, and that got cached, though it’s really a cookie issue.)

But for performance? Leave the caches alone! It just amazes me how many people empty their web browser’s cache every time they’re done using it, and then wonder why everything is slow. It’s because, in their misguided quest to optimize their computer’s performance, they just deleted all the files that were there to optimize its performance. Even more ridiculous is all of the advice about cleaning out the Windows Prefetch data for performance. These people clearly have no idea what the Prefetcher is, because deleting all the files is about the worst thing you can do for performance.

Of course, this doesn’t mean that programs like CCleaner aren’t valuable. There is a lot of cruft that Windows and its oft-used applications build up that isn’t needed. But that’s really an entirely separate issue from purge all of your caches, all of the time, because CCleaner’s strength isn’t in purging caches, it’s in finding totally useless cruft on your filesystem.