Why does your Agreement with clients extend for an "indefinite term?"

I do not set a specific time limit on my relationship with my clients because it is impractical. A novelist may write twenty novels, a nonfiction writer may have their work revised and updated, and a college textbook author may see their work extend through ten editions. What time limit would satisfy my varied client list? If one of my clients is unhappy with my agenting, they can terminate our Agreement simply by sending me a letter of notification. The Agency can terminate the Agreement through the same process. I have found this approach much more efficient and fair for both sides.