You're a professional creator who makes a living off your creative works. You want to be paid for granting rights, but you may also want to hold onto as many rights as you can in order to maximize the returns from different ways of exploiting your work. You may have to deal with commercial distributors whose interests may differ from yours, especially as time passes and new media lead to new ways of exploiting works.
If you are creating works for a living, payment is paramount. Some contracts offer one-time, lump-sum payments; others give an advance and then a stream of royalty income when (if) the advance is earned back; still others provide for royalties without an advance. If your contract provides for royalties, you want to make sure you're being accurately paid for your grantee's excercise of whatever rights you granted. See About Royalty Statements.
