Hi,
I had been having some intermittent errors on my site when trying to add/edit pages.
I've now removed an add-on which wasn't being used and that problem 'seems' to have gone away, but I've noticed there are loads of files appearing in my cache, particularly .lesscache files. (screenshot attached)

Does this mean there's something wrong with my .css?

Clearing the cache through the dashboard removes them but after just a few edits they are all back again.
Also what's the 'expensive' folder for? Clearing the cache doesn't remove it.

There's also loads of files in the cache/thumbnails folder which also don't seem to clear (second screenshot).

I have some more content to add to the site but I'm a bit nervous now I've noticed these files.
Many thanks
Allison