For example, to resolve combat (a rather common event in a lot of roleplaying games) a simulationist approach might be to see if the character hits, then if the victim can parry, then how much 'damage' the weapon does, then how much of this the armour stops, then determine what part of the victim is hit, then see how much harm the remaining damage does.
The benefit of doing it this way is that its simple for the players to interpret the results and understand what must have happened. The drawback is that the process takes a long time to perform and the process is not really how the real-world works anyway.
GURPS is often classified as a simulationist role-playing system.