I try to clutch most of the time, but if I run into an obstacle that requires a quick shift up or down, I will not use the clutch.
When riding in deep sand that requires one to get into second gear to start floating on top, I will not use the clutch to shift up.
When doing a hill climb and I start to loose control or gut out and need to shift down, I will not use the clutch. Also if there is a very short run up to a hill climb, I will not use the clutch to shift up.
And sometimes it is just fun to give it to see how quickly you can get going - Wee included.