They may dry out if you reheat them after freezing, but you really can't beat the convenience. Especially if you're going to reheat them in a sauce that can help add some moisture back. This is also great if you're only reheating a few at a time for quick meals.  If you're going to make them ahead of time for a party, I would freeze the raw sausage balls for best quality, so they're cooking for the first time before you serve them.