Is it advisable to calibrate the battery on a MacBook? How useful or necessary is it to calibrate the battery on a MacBook?

If it is, should it be carried out when first purchased and does calibration of the battery mean it will also last longer?
There is almost no value in a user trying to "calibrate" a unibody MacBook's internal battery since it has multiple cells and the system handles this continually.

Older MacBook that were non-unibody construction with removable batteries did benefit periodic calibration runs to update the Mac's estimation of time remaining. Calibration didn't actually give you more power, just a more accurate estimate of the time remaining before that battery needs a recharge.


The canonical reference for which models can benefit from calibration is Apple Portables: Calibrating your computer's battery for best performance. 
A nice primer on battery technology in general is Apple's Lithium-ion polymer batteries site. 
For more technical data, I like reading at the "Battery University" site.


If you seek to extend the time between when you buy a battery (or computer) and the time when it needs to be replaced three things will help prolong the useful life of your battery.


Discharging it until the Mac sleeps at least once every month or two.
Not letting it drain totally for months.
Avoid exceeding the re-charge cycles (new models typically are rated for 5 years and 1000 equivalent charge cycles).
Avoid storage in very hot temperatures and use (charging / discharge) in hot temperatures.


In the end, you might pay between $100 and $150 for a new battery, but something that happens once every 3 to 4 years, Apple's new battery technology is far better than the old days where heavy users needed a new battery yearly and failures were far more common.