It depends where they are. Some games uses asserts at a very low level to check things like ensuring that vectors or matrices are valid (to some expected proper

It depends where they are. Some games uses asserts at a very low level to check things like ensuring that vectors or matrices are valid (to some expected properties) after every calculation. This is very useful for bug fixing, but means you suddenly have asserts in the most performance intensive of inner loops. Now those particular asserts aren't often turned on the default debug build, but turning them on will have a significant effect on performance.