I've used the GameTime passed to Draw for visual effects that don't need synchronizing with the main game. For example, I want a sine-wave based pulsing glow around some object. If I wanted to track time for that in the Update method, I'd need another variable somewhere. Or I can just use GameTime.TotalGameTime and be done with it.
You certainly don't want to mix in critical gameplay-impacting rendering this way, but for any visuals that need some long running time variable, it's a free way to have that handed to your drawing code.