To extend Daves point on clamcleats for kickers.
A cam cleat can be pulled out without having to pull the rope itself with more strength, and clam cleat has to be pulled more before it can release from the cleat.
So when you want a kicker OFF in a hurry, maybe the cam cleat works better.
On the other hand, if the rope in the cleat is going to get move pull on it, like a genoa halyard box, then maybe the clam cleat would work well.
As the more tension you put on the clam cleat, the further the rope gets pulled into the clams.