If you can, then there's no real need for using a one-time pad. But there's a benefit that comes from a fact that exchanging the random data is a completely separate process in time and space from sending the messages. You can do it once, spending all your resources to secure it. Imagine e.g. two governments establishing a secret emergency line by generating a few terabytes of random data in one physical place and then escorting each copy in armoured trucks to proper communication factilities.

BTW. exchanging physical "XOR's" for one-time pad communication is a plot point of Vernor Vinge's "A Fire Upon the Deep".