If you really really don't use battery, if you want, before you open your cMBP for the first time, you can open the back cover, remove the battery cable from the board and leave the battery inside as new (rMBP will be harder to unscrew because Apple put in a special pentalobe screw).
But keeping battery inside and keep the magsafe plug-in at all time shouldn't degrade your battery much, assuming your don't accidentally trip over the magsafe cable sometimes. :roll eyes: Battery will also serve as your UPS. You will also be good to go whenever you need to be portable. Though, you should cycle your battery (let it drain to 5% and let it charge up) like once a month or once every a few months, because the battery cells will start to degrade on first used (that is when you plug magsafe in for the first time). That would be just a few cycles per year.