We used a cert over Christmas break and also have booked in a location with a very large event taking place in the middle of summer.

We've never really had a problem finding a place to use them. However, I do agree if you are trying to book a TS property of beach club for spring break and don't book early enough that could cause an obvious issue.

To the OP,
Welcome to FT and hopefully you will come back and post more specifics to see if some of the very brilliant travellers here at FT can help you or give you some of their knowledge.