And the reason to not regrind the top is so that tool height (with respect to the workpiece) is not changed. With QCTP this isn't as big an issue, but with 4 place (standard minilathe) TP it means you have to readjust the tool by shimming.
A quick pass with a stone shouldn't change the height by enough to bother with, but if you grind it, it's going to have to be reset.
Just thought I'd clarify the reson not to grind the top unless really necessary.