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I always put it to sleep and only shut it completely off when necessary (updates, etc.).
 
Neither one is better per se, but if it's any consolation, I always leave my mbp sleeping, and it's served me well for over 3 years.

I love not having any downtime, and the ability to leave things like iCal, Stickies, and Mail always "up."

Just keep your computer updated and you can leave it sleeping for as long as you like. 🙂
 
Sleep most of the, like when going back and forth between home and the office. Power off on long trips.
 
I think a combo of both is best. Sometimes I'll sleep it for a night or two, then shut it down, then sleep it for a three nights, then shut it down each night for the next two, etc. I just do what I feel like, it's good to shut it down to clear the RAM.

FWIW if traveling I always shut it down because I don't like the idea that something just might wake it up or go awry and then have it overheating itself in its sleeve in my bag for hours...I shut it down purely for precaution.
 
I always sleep my computers unless I won't be using it for more than a couple days then it gets turned off.
 
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