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 battery since it has multiple cells and the system handles this continually.
Older MacBook that were non-unibody construction where you could have two batteries and exchange them did need periodic calibration runs to update the Mac's estimation of time remaining. You didn't actually get more power, just a more accurate estimate of the time remaining before that battery needed a recharge.
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.
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.