Some boards have molded fins and it allows them to track well without the center fin. It will ride like a normal board just looser. Fins provide tracking and that is good. Unless you are advanced and have great control & a board with molded fins I'd leave the things on there.
depends on the trick, if you have plenty of control finless then why switch? Fins can have a tendency to straighten you out too fast and a finless board is able to slide into position easier, on the flipside this can work against you too.