Just my 2 cents:
Biggest benefit: Clam plate adds a bearing between the KDrill and the M18 (or whatever drill) which, in my opinion, is a good thing for eliminating or at least minimizing impacts on the drill itself. None of the downward force/impact is placed on the cordless drill itself.
Clam plate allows you to securely bolt the KDrill on, not just use the chuck which can come loose and “ploop!”. See an earlier post about now the KDrill does not really float despite having the foam float on it. With Drill plate, it’s bolted on – another good thing IMO.
For most of us used to a gas auger, the drill plate makes it a seamless transition in terms of handling. Plus makes it easier and probably safer for use by those not familiar with ice augers. I wouldn’t hesitate to hand the auger to a kid who never used one before, but I might think twice about it without the plate …