PageSpeed offers three base levels of optimization:
OptimizeForBandwidth. The CoreFilters set contains filters that Google's PageSpeed team believes are safe for most web sites. The OptimizeForBandwidth setting provides a stronger guarantee of safety and is suitable as a default setting for use with sites that are not aware of PageSpeed. The default level is CoreFilters, to disable use the PassThrough setting.
Enabling, Disabling And Forbidding Specific Filters
On top of a base optimization level filters can be enabled, disabled or forbidden.