Taking great care to perfectly align an enlarger is like using a tripod when the conditions allow, instead of hand-holding: the best and easiest way to significantly increase sharpness. I personally try hard to have sharp grain in my prints.

I align my enlarger every 20-30 or so hours of printing or whenever I bump my head into it in the dark.

This subject is quite similar to that of depth of focus, something that can be important when there is doubt the film cannot be held perfectly flat. Assume the tolerance converges to 0 and be happy with prints that are always sharp (from a technical point).