Anybody care to discuss the various attributtes of flare on the sides?

I see all boats have flare fore and aft of the cockpit....some boats
have pretty flat sides at the cockpit..some have flare.

My Petrel has flat sides at the cockpit..has very good initial stablility
and i'm not experienced with enough boats to say how good the secondary is..seems good.

What will flare at the cockpit add? (besides drag)