I must admit in so many playthroughs, I've never thought of using those grenades. In what context should I consider using them? If your Stealth skill is low, won't you just immediately get found on the enemies' turn?
I suppose it could be useful with high stealth if you can't LoS or incapacitate your enemies, but you have enough distance to be safe. It could also help activate stealth abilities, like Snipe.