Just because the metronome is running doesn't mean you have to hit every beat the same time it does. It's telling you what your overall tempo is.

I know two extremely high-profile players who keep their foot tapping with metronomic regularity. The point of this, the way they see it, is not simply to keep at a steady tempo, it's get a feel for when they're ahead or behind the beat, and to what extent (and they WILL be one or the other much of the time). It's something I haven't properly learned yet but mean to.

Almost all Highland pipers keep a foot-metronome going. I'm not sure how most of them perceive what they're doing. But this includes all the big names and all the ones you would least accuse of being metronomic.