Sparck - good questions!
It seems that both of these new features were added at the request of another CATIA-using company, probably to to allow for data migration.
From previous posts, most companies (most users) do not enable Hybrid Design because of the confusion it creates for existing data and users (like you) that are experienced with older releases of V5. There appears to be little benefit to use Hybrid Design.
Likewise with Volumes, there appears to be little benefit, since most (all?) of the volume options can be done directly with solids in Part Design.
Do a search on both for more posts