This will depend on your goals! As a general rule, HIIT should only be done 1-2x per week. True HIIT is all out, and it's not possible to train at maximum intensity every day, as the body needs time to recover. Steady state cardio can be useful during the last 1-2 weeks of leaning down, but shouldn't be used regularly. The body becomes accustomed to any workout that is done regularly, so the more cardio you do, the more cardio you'll need to do in the future to see the same results!
- Erin Stern, 2x Ms. Figure Olympia