It's mostly important to take a day off if the intensity of your workout is very high. For instance, if you do strength/resistance training, it is advised to take a few days off before working out the same muscle. You can, however, do resistance training every day if you just keep hitting different muscles ever day. That way, you're giving each muscle at least a week to recover.
If you think my post is too abrasive, harsh, or offensive, you're:
B) Too sensitive.
C) Not going to receive an apology for pointing it out.