2 important things;
1. make sure you have a page caching plugin (in which case the autoptimize impact only occurs on first page load and this site is blazingly faster after that)
2. make sure you don't have a plugin that is inserting page-specific CSS and if you do, make sure to exclude that CSS from being aggregated/ minified (this is closely related to the FAQ entry about cache size & autoptimize not purging automatically).
hope this helps,
frank