The sneak skill in Valheim allows you to travel unnoticed at the cost of stamina. It actually uses a tremendous amount of stamina to crouch walk in Valheim so you have to use this ability tactically, or have a massive stamina bar from eating lots of good food.
Effects of leveling sneak skill
- -.33% stamina cost while sneaking per level for -33% stamina drain at level 100 (max level)
- Noise reduction with each level for complete silence at maximum level
It's hard to gauge noise reduction per level, but we know at max level you can walk up to enemies and punch them without fail.