When does a Throwout Bearing spin and when does it not?

Does it spin all the time?
Does it spin only when clutch is engaged?
Does it spin only when the clutch is disengaged?

It spins while you are holding down the clutch pedal (disengaged)

You sure? Seems to me it would spin with the disc when it's engaged or it would spin all the time....hmmm.

It spins all the time, but only see's a load when you step on the clutch.

The inner race of the throwout bearing is always in contact with the release plate fingers, although only lightly when the clutch is engaged, like nj says. But enough to keep the inner race spinning at all times.

The outer race doesn't spin, of course.

Should make contact with the fingers and spin all the time.
However, sometimes it may retract a few microns too much, and it won't engage and spin until you press the clutch pedal. This often times produces a squealing noise as you start to push on the pedal.