Stealth give you the advantage of scouting the enemy undetected. You find out their numbers, positioning, patrols, equipment. Then you can devise a good plan to take them out on your own terms, selecting the right weapons, utilities, armor etc for the job, place traps, use a good position and get a deadly first strike. This is an awesome ability, that you pay for by being lightly armored.
When played well, planning combat from stealth means you have already won when starting combat. Sun Tzu would be proud. Feats like Blindsiding or Snipe just enhance the power of stealth even further.
Maybe it's my lack of experience showing, but that only seems to be true for the beginning round of combat. After you've broken stealth, you are a squishy sitting duck. Someone tosses a grenade and you are reloading the fight. It's why I'm usually reluctant to play low health low armor characters.