So, if you are a professional photographer, is it OK to NOT take a photo on any given day? If you are a professional, SHOULD you be taking photos EVERY day?
In a word: "YES!" It doesn't matter what the subject is. It can be a big self-assignment, or it can just be your family, or something you spot while out walking with your camera. You don't even have to save the files if you don't want to. The important thing is, you're out shooting.
Shooting every day gives you a chance to develop your technique and your eye. You learn what looks good, and what doesn't. You learn what the best way to photograph a certain subject is. You get a chance to try a new technique you read about, or a camera setting you've never used before. And hey, you may even get an interesting photo out of the deal.
Shooting is practice, the more you practice, the more proficient you are handling your equipment. You also pick up on the idiosyncrasies of your equipment. The camera really does become an extension of yourself So when the pressure is on, and the client is watching, you're not sitting there fumbling with your equipment.
Shooting every day also makes sure you have some lasting memories. It is too easy to get wrapped up in "assignments" and "Professional Photography", that you forget to get those "Kodak moments". You end up with lots of photos of other people's families, and none of your own.