As you read that thread that Nick pointed to, make special note of Post #13. Pendlewitch got it all right in that post. The chemistry of modern batteries used in the MBP line is not what used to be in the older batteries and does not need the deep cycles that Ni-Cad batteries needed. In fact, LiIon batteries like in the MBP prefer fewer deep cycles. But they do start to decay slightly at about 2 years after manufacture, no matter how gently treated they may be. But that decay is very slight at first. According to coconutBattery, my battery was manufactured March 16, 2011, making it 1688 days (4.6 years) old. It has a design capacity of 8450mAh, but presently has a max charge of 8026mAh, about 94.8% of design. But in the time I've only used the equivalent of 62 load cycles because the MBP is on external power almost all of the time. I do use the battery when I am traveling or when I move from my office to the coffee table to control my Apple TV with it. As you can see, even with very gentle use I've lost over 5% of capacity, so batteries eventually decay, even if you treat them gently like I have.
The reason you'll see Apple recommending one deep discharge each month is that that discharge will calibrate their battery management indicator for you. It's not for the battery, it's for that software. I don't bother and the error in the indicator is practically zero. So I would say you can safely ignore Apple's advice on that part. If the indicator of charge or time remaining becomes erratic, then you can charge it up full, then discharge it deeply to do that recalibration. Otherwise, leave it plugged in if you can.