We loved our cabana for our summer visit (August 2012). We had a very hot, bright, sunny day and it was pure pleasure to be able to get out of the sun at our leisure in the afternoon and enjoy a little siesta after frolicking in the water all morning. It was the ultimate indulgence to make our day of relaxation exactly that. We did not have a dolphin swim that day, so we weren't having to work our activities around that commitment.
For our first visit (January 2012) we did the dolphin swim and while the weather was gorgeous, it was not stifling hot. We had no cabana and didn't feel we needed it then.
If we go back again some day, I would definitely rent a cabana if the budget allows. We loved having a home base to return to that was private and cool. We also loved the pampering of our personal attendant....she was awesome and tended to everything we needed.