Stealth is useful both in combat and exploration (when traveling through dungeons or opening chests). It allows you to find and disarm traps. In some cases in scouting mode you will find secret switches that open secret passages. Thanks to that you will greatly shorten your road to the target or get to a room with treasures. During combat use scouting to learn of position, numbers and strength of enemies. Keep an eye on the circle around your character, it will be gradually filled first with yellow, then red color. Yellow means enemy hasn't spotted you yet, but is suspecting something. Red is a warming that enemy has seen you.
Before battle send only one character on scouting, the one that has highest stealth level. It will allow you to retreat any time you need. It takes more time, but is more effective than sneaking at enemy with whole group. You can travel with whole group in scouting mode when you're walking through dungeons and search for traps.
Important - Some of the most complex traps and secret stashes may not be discovered by your scout if his Stealth skill is not high enough. This means you should be working on increasing this skill from the very beginning of the game. If you really want to get your hands on some secret treasure during your first visit to a location where it's hidden then you can use potions as an alternative solution (like the one which temporarily increases the character's perception).