It's getting late in a tight game. You've been trading blow for blow, countering each other's allies, weapons and draw engines. You have an Adlar in your hand and draw a Book of Curses. You sacrifice the Book to get to six resources since you already have one in play and grace your empty board with Adlar the Just. Right? Wrong!
There is a world of difference between holding one (however useless) card and passing the turn empty handed.
Being empty handed gives so much information to your opponent. Since you played 1 Tidal Wave already, he knows you have at best 15% odds of drawing another one in your remaining 20 cards (3/20, if you carried 4 and did not sac one early). Even if you have a Wizent's Staff out, it's still pretty easy to evaluate your odds of drawing a card (in this TW example, roughly 1-(5/6 * 5/6) = 1-25/36 = 11/36 = approx 33%). It's also easy to know the maximum amount of damage you can deal next turn or that you can't swarm the board. You're also highly unlikely to have item destruction.
If you however happen to have one lonesome card still in your hand, it makes it much harder for your opponent to plan his turn. He can't know which card you top decked and has to assume that that one card you've been holding onto is key. He has to be much more careful which might buy you enough time to rebuild your hand or your board.
Basic tip: Carefully consider the situation each time you might end up with an empty hand. It might be worth it, but you don't want to hand your opponent an advantage he doesn't deserve.
Intermediate tip: Become familiar with your opponent's class card pool and the current metagame. Try to anticipate his best possible top deck.
Advanced tip: Learn to quickly estimate probabilities to maximise your plays when your opponent is in topdeck mode.
Originally written by FDL: http://www.shadowera.com/showthread.php?16952-FDL-Tip-01-Empty-Hands-Empty-Threats