For evaluation of skill as well as a way to practice in confused/technical wave conditions.
Oahu (Makapu'u Point or Hanauma Point?) photo: Darryl Khng video
There are specific locations around the world where there tends to be confused water and/or rebound that either provides a challenge to a paddler's stability or can prove to be unmanageable in terms of one's ability to stay upright. Some of these places with the right intensity and safety conditions/support can provide a useful gauge for your readiness to paddle in bigger water or on runs that have similar sections. Some high quality runs do have significant sections of rebound going past steep shorelines or docks that you have to be capable of paddling through to reasonably justify your being able to do such a run at all.
If you can't maintain decent paddle technique then don't screw up your technique just practicing getting gripped in these kind of conditions.
Beyond assessing your paddling technique through slop, also practice and assess these:
Oahu - Makapu'u Point and Hanauma Point
Darryl Khng
(The locals say this gets far tougher when the swell gets bigger than this)
English Channel - Mouth of the Arun River
Tom Mason