We seem to have the pro insurance side covered pretty well... now I'll put my 2 cents in for the other side.
I've been flying since 17, built 2 planes and traded for my current Kitfox. On all my planes I've carried Ground - not in motion. Even for the first flights and first years of ownership. Cost is a large part of the equation, however I also have a general aversion to insurance, and figure I trust myself more than the insurance company does. We both don't want me to crash. I like not in motion for the things that I have no chance of influencing...
Just another data point. Everyone has to decide how they want to go about it.