Add to what others have said, flight lets you bypass certain class abilities or environmental hazards. For example, you can fly right over an invoker's quicksand, iceslick, grease, or dug pit.

The danger of being tripped is not that it damages you (because damage isn't generally significant, in most cases) but because it prevents you from running away (since you can't perform an action for 2 rounds, and that action might just be "e" if you happened to be walking east along the eastern road).

I gotcha. My prior mudding experiences have trip as a very weak skill... definitely not two rounds of lag. Thank you both for your answers.

Specifically it allows access to some areas you wouldn't otherwise be able to reach (Arial City as an example) and means you don't have to have a boat to cross water (but you always should anyway).

Not being able to be tripped is a huge deal though. Every melee class gets trip, and two of them can trip you to death pretty easy if you can't fly. Trip is also pretty reliable, so it's an easy way to get ganged down in a way that you can't do much about.