Discarding cards that don't help you but could help your opponents is a smart bluffing tactic. You can use this to trick your opponents into thinking that you are about to declare "Rummysaata" and force them to hold onto certain cards or alter their game plan. Bluffing can also be used to deceive your opponents into believing that you are attempting to form different sets and runs. You can make it more difficult for your opponents to predict your moves & more difficult for them to form their own sets and runs by discarding some cards and picking up others.