Stealth is usefull only as an opener, so it's useful to approach a boss type enemy (troll, abomination) and use the alt-attack on them with a dagger to almost one-shot them, making the fight a breeze.

It takes some patience, because stealth in this game is simulationist: it removes the sounds you make approaching, but if they see you they detect you. It's not the "invisibility circle" most games pass as stealth.

Also...you can get the backstab bonus if the enemy hasn't detected you, so shooting from afar with bow gives you x3 damage.