An improperly staked gas key will eventually work itself loose and the rifle will go from semi-auto to single-shot. Not good especially when you're going through high round counts in a single day like a tac-rifle class for example.
Properly staked on the left, improperly staked on the right.
You might want to check that the buttstock retention nut is staked properly as well.
Why should you have to check anything even if it's shooting well? It's called preventative maintenance.