Haha....Yes, the leadins "are" supposed to cut. In this case you would not want the cutter to plunge directly down onto the finished path because the cutter will tend to gouge the profile. The recomended method is to plunge away from the finish profile and then feed into the profile through a gradual arc and then gradually move away at the end of the profile. The other variations are for times when you don't want any leadin/out such as a radial slot. I hope this is clear now.
Andy