I would say its not a “this or that” answer. I think if keep a client too long, you run the danger of becoming complacent or relaxed. You build a relationship that becomes like a friendship. The “coach” feel is not there as much. They get in ruts just like we can get in ruts. When you have to wear so many hats and constantly motivate and bring people up, who are constantly down, it takes its toll. Sometimes you get tired of pulling them along and hearing every excuse in the book that your eyes glaze over. You can want it for them, but you can’t go get it for them. I think, unless there some specific goals (athletes, etc.) 4-6 months should be a time to start “cutting the cord”. This way they should be at their peak enthusiasm, provided they were truly committed in the first place
I agree with Karin that money is the reason that many clients stop training. Money is oftentimes also viewed as the reason that many potential clients never START training as well. Second would be their “perceived” lack of time. I say “perceived” because I’m a firm believer in the fact that we all have 24-hours in our day and it’s how we allocate those hours that matters most. We each FIND or MAKE time for things that we perceive as important to us. I’ve worked with very busy surgeons, or business owners who have MADE the time to train because of its importance to their health, while you have others who will find any reason or excuse NOT to have time for their own health.
So, in my opinion, the answer is money (first), time (second).
I hope that this helps.