As per subject line. I installed Autoptimize, it looked like it was working (doing a view source on my home page) and did seem quicker. A few hours later I got an email from my webhost saying that I was close to my disk space limit. By disabling Autoptimize and removing the cache directory I was able to reclaim about 80Mb of disk space.
The description didn't make me think that it cached a lot of data. If this is by design then some way of limiting the amount of space used is really needed. If not, them I'm happy to help debug with you.