I'm in pretty good shape and play tennis 3 times a week. I've started this HIIT exercise and was wondering does anyone do this everyday? What would be the benefits of doing HIIT everyday? Am I just spinning my wheels doing HIIT that often?

I do some form of HIIT 5 days a week. I bike and run. I'm not sure if its *bad* although I bet you'll get a lot of people on here saying they don't advise it. I think if you're already in great shape you could work up to everyday but doing it suddenly and all at once would be a bad idea. You'll develop injuries for sure.

If you don't already, you might want to consider implementing a full body strength training routine 3x a week.