It gives you the right to use a bull and not have to purchase any non-owner bull permits when registering calves. Not all breeds have this. The Red Angus Association has it, and it will ussually cost you $35 to $40 to register offspring if purchasing semen and then bull permits.
If you are buying a bull hoping to sell semen, that is ussually all the farther it goes. Hoping... The competition is really tough in the semen business when Genex, ABS, & Select Sires will drive into your yard and fill your tanks with nitrogen and deliver the semen as well. If you sell some privately the purchaser will ussually have to pay for shipping and that will cost around $70.
I recommend that you buy one to use and then maybe you can sell some semen as well.