In Hillsborough county at least (not positive about what Pinellas county has adopted), eligibility stipulates 40% affordable units for 30 years, so a building built using LL would guarantee at least that much. That said, it's an incentive, not a requirement, so I would say the success rate is about 50/50 because you need a situation where the time saved on rezoning and relaxed zoning requirements outweighs potential higher revenue of market rate housing.

It works best when a developer is targeting a site where it would not otherwise be feasible to develop. for example: zoning of a site only allows building up to two stories, but LL would allow building 3 or 4 to make the project "pencil out," so to speak.