Ruth, I just don't want to change my diet too radicially as I have a really big competition coming up. Essentially, losing too much weight in a short amount of time might jeopardize my performance, and I don't want to risk that. But on Feb. 29th I'm starting Phase 1.
Edited to add: Also, in one of his interviews on the Prevention site, Dr. Agatston said that people exercising for 90 minutes or more at a time should eat a low-glycemic carb (like oatmeal) before working out to give them sustained energy. My season will be over soon, but I do two 120 min workout sessions a day, and I don't think Phase 1 would give me enough carbs to sustain that kind of intensity.
He also said that people who only have a little weight to lose can start on Phase 2, but he didn't give too many details about that. I weigh 115 pounds at 5'1'', so I really don't need to lose more than 10.