[JohnBraden]

With the rail pass, you can reserve a seat on those JR trains. If you don't reserve a seat, you have to wait in line (get there earlier) at the station and it's first come, first serve. With the pass, the reserve price is included, so one might as well reserve it.

If you don't buy the rail pass, you can still bypass the reservation additional price by lining up on the track where the non-reserve seat cars will stop. But you have to realize many people do the same, so if you're doing it at the terminus station, then get there early. If you're somewhere in the middle of the train run, then it all depends on the time of day. Most trains aren't completely full on the Tokaido Shinkansen.