I'm assuming (Oh-Oh) that you are talking about workstations.
There are so many reason pro and con, it depends on what you are trying to accomplish. Does a workstation need to be shutdown? No, I have some that have been running for weeks with no trouble. Is it good practice to reboot once in awhile? Of course. Memory leaks and other problems can be kept under control through a strategic reboot. I myself prefer to shutdown workstations at the end of the day, if for no other reason, to conserve a little energy.