Never. How many times I got them killed? Too many to count.
Quoted for truth.
Even on my sneaking characters, they always seemed to lag behind and die to some trap.
Went through a whole dungeon thinking Lydia was right behind me, turned around and was like, "Lydia?"
On the way out, find her corpse lying not far from where I placed a rune at the entrance.
I think traps are magnets for followers, really.