I've been thinking about this a bit in my own training. The "pump, rush, and dump" phrase is a great one Lynn...and describes something I've felt in some uncontolled situations. It usually leaves me feeling a little sick and very weak.
On the opposite side, in aikido practise, especially against very solid empty hand attacks and even half decent weapon attacks, I've felt something quite different. It is more of the fudoshin (imperturbable mind, steadfast mind) that someone else alluded to. There is a sword version of ukenagashi that I was taught where uke crosssteps in to do a front cut, shite meets their cut, enters to the side and allows uke's cut to give power to their own cut. With a strong committed attack, I sometimes find it difficult to actually meet uke's blade and present a good target, only moving once the timing is correct. I either move too soon, allowing uke to track me (usually moving out of fear of getting hit), or wait too long and actually get hit.
When the technique works well, my own cut is calm, very powerfull, and I am able to generate a deep kiai from my belly. When my timing and mindset are off, I can hear it in my kiai, even if I hide it in other ways.
I think at some level, there is a need to face this kind of fear, and to learn to overcome it. Or face it without the "pump, rush and dump" reaction, which destroys any idea of zanshin (remaining mind) for me, at least.
I guess I'm saying that I find a use for fear in practise, as long as there are agreements between shite and uke, for how this should take place.