To answer your question, keeping pinkies in the freezer is very convenient, you don't have to feed them, they don't make any noise, and whenever you need one, just thaw and serve.

I have also bred and raised mice, and it's a mess, it's hard work, and my snakes don't seem to really prefer a live mouse over a thawed mouse.

final thought, Garter snakes swallow them alive, they do not kill their food like constrictors or venomous do, they just gulp it down alive.