you have to use the open book to see the size that will possibly come in. Also it is a good indicator to see if a size is chasing, COMBINE the open book with the level two MM and you have a good strategy going. Basically for me the open book gives me a reason to be in a trade and reason to get out of a trade.
I use regular market depth And Level 1 Bidsize AskSize mostly for liqudity though although I'm proabbly trading blind though