The autoptimize cache is a tool that we use to improve performance.
Sometimes, it will grow a large cache (store of optimised files) that can be purged.
You can DIY this with no negative impacts, aside from the cache having to rebuild, which you will not notice. To do this, simply select Autoptimize in the top menu and then select Clear CSS/ JS Cache.
If we can help with anything else, please let us know.