Hibrenate or sleep, uses barely more power than having it off. Most of the newer laptops consume only a couple watts when in a low power state, about as much as the power supply does doing it's checkup on the battery. Fans also shutdown for the most part in sleep mode, hard drives spin down and for all intents and purposes the machine acts like it's off. The big advantage is being able to hit the power button and resume what you were doing in just a few seconds.
I let all my computers go to sleep and just restart them once a week or so, I have a couple that are 6-7 years old that work just as well as when they were knew.