From my understanding:
a. Form of active recovery, helps to enhance blood flow. Purported benefit by many on this board (not saying I agree or disagree with this) is also that tempo runs increase capillary density. This helps to increase blood flow also so recovery on high intensity days between runs can be possibly be faster along with the ability to keep the body “warmed up.”
b. Can help smooth out technique issues, however, the chances this translates into corrected technique at full speed is not guaranteed and probably not likely.
c. Not sure a whole lot changes with tempo during peaking. There will be more days of it in the taper as there are less high intensity days, but I don’t know how much the volume of tempo decreases.