Pumping works. Really. It works.
* Fascial stretching (necessary for growth)
* engorgement with lactate to stimulate igf-1
* better vascularity
As far as being sore, I have always tried to avoid this by warming up and stretching afterwards. By doing hot/cold intervals in the shower, and by having a good shake right after I come out of the locker room.
Stuff to do for a better pump:
* Less rest between sets.
* stretching, squeezing, and flexing out during and after your WO.
* handstands/headstands. Handstands will pump up your forearms and add vascularity to them.