No, you do not need to use this command if that is the default for each switch port interface under the newer IOS.
It doesn't hurt, though, especially if you have switches still running older IOS code, or if you have played around with changing that priority from zero to something else.
The switch won't show you the priority command line unless you change it from the default.
To test this, do the following. On one interface set it to the next-lowest priority, 1, then exit config mode and look at the running configuration for that interface. You should see the priority command line. Next, go back into config mode, set priority back to 0, exit and look at the interface's running config again. Priority command line should be gone.
Hope this helps.
