If it's stuff that's visible on the field, yes. If it's against the AI, sure. The one situation I won't is if I'm in PVP and don't want to reveal something in my deck that I don't need to win. For instance, if I'm using a speedbow with purifies in CL, and I have cards in hand I could play but don't need to win, I'll hold on to them, unless it's something obvious, like playing a black hole in DBH on the last turn. Stuff like purify, reflective shield, and other things that could potentially alter a game completely are the sort I'll hold back in pvp if they aren't needed.