Power Consumption: when is it better to put macbook pro to sleep vs. shutting down?

I wouldn't be particularly concerned with the power consumption of your MacBook. Assumming you run the system full throttle (meaning the CPU usage is maxed out by doing something like playing a highend game or transcoding video) and you are using the full 63.5 watts constantly for 24 hours a day and 7 days a week... your annual cost would be about $110 (with a relatively high cost per kilowatt hour of about 20 cents). Realistically, no one uses their computer like that and it wouldn't last very long if you did. A more reasonable estimate would be maybe running at about 50% power (we'll say about 30 watts) for maybe five hours a day. Now you're looking at about $11 a year (less than $1 per month)... and that is with the machine on for a full five hours a day... every day... under moderate use. As you can see... even with using the machine regularly, there is a fairly nominal impact on your overall power usage. With the machine sleeping, you're talking pennies a year.

So, cost is a non-issue. Even in terms of just conserving energy for the sake of being green, your MacBook has little impact. In terms of what's best for the machine itself, most people just let their systems sleep. It will use more power powering up than waking from sleep... but this is such a brief period as to make the difference almost immeasurable.

The only time you really "need" to power off your machine is when you do an update that requires a restart... or if you are going to be away from a power source for an extended period and you want to conserve every bit of power to maximize your battery's charge.

I shut my macbook down about 1 time/week and it's doing fine.

Chris