Despite being a robust feature of the 1.9 branch a key element of this functionality has been deprecated in 2.0.x and 2.1. See
My understanding that 1.9 Groupings were NOT experimental and only remained in that part of the admin menu as there was no obvious place to re-locate them.
In 1.9 groupings were available for all activity and resource types. This functionality doesn't make much sense if this is not the case.
Groupings are used widely across the activity and resource range, demoting a significant part of their scope to "experimental" is retrograde step that
reduces confidence in Moodle.
The ability to manage differentiation of all types of course content i.e. resources and activities needs to be fully (re)implemented at the earliest opportunity.