Searching isn’t free – it takes a turn. This means duration effects go closer to expiration, and that there’s a chance wandering monsters in the area might take note of you. So it’s not something you’ll want to do willy-nilly every few steps. But when the situation warrants it, you can be initiate a search via hotkey, or by clicking the magnifying glass in the command amulet in the lower right of the screen.
Searching gives you a chance of discovering anything hidden nearby. It uses the best skill of everyone in your party. Particularly valuable in the case of traps and ambushes, it allows you to discover them without setting them off. If you discover a trap, you’ll immediately be taken to the trap-disarm screen and given a chance to deal with it. If you discover an ambush, you trigger the combat immediately – but the would-be ambushers do not get a free surprise round to attack you with impunity. For secret doors – well, you are simply alerted that there is one nearby, so you can poke around a little more carefully.