When I go into a lower dungeon, I expect some people to be new. I ask if they have any preferences in how it should be run. If someone is a new healer, tank or dps it might be faster to just take it slow because many are not quite adept at a speed run yet. I do these when I have extra time or just bored. When I first started the game, I got to watch all the CS's because everyone else was new too. I go in expecting that, but ask if people want otherwise. It saves frustration and meaningless fights down the road. Plus, usually gets people talking if they realize that the guy in i100+ gear is not going to ruin their experience.

Personally, I love to mentor people, I get great satisfaction from it when someone is appreciative. However, this is depending on my mood mostly and my patience at the time.