It all depends on the course. If your course is 7200 yards long from the back tees, you have to have at least 4 sets, unless you want 1000 yards between sets. I would think the "ladies" tee needs to be around 5200 yards MAX. So with 4 sets, you are looking at something like 5200-5800-6400-7200, and that looks odd. If you only have 3, now you have 5200-6200-7200 and that looks VERY, VERY ODD. The longer courses get, the more tees they MUST have in order to make the course playable for all customers. Now, if the course is 6500 from the back tees, its a different idea. 5200-6000-6500 is fine. But if people continue to insist on terribly long courses, you will continue to see 4, 5, 6 maybe even 7 sets of tees. (I have never seen 7 sets, but I think I have seen 6, and 5 is almost normal these days)