'So in other words I should charge it fully, unplug it, use it until the battery runs out, then charge it up again?' - more or less, yes.
But you can leave the MacBook Pro connected after it is fully charge, from time to time.
Just allow the battery to full discharge, instead of constantly connecting the MacBook Pro to the AC / DC adapter.
You can remove the non-fully discharged battery, from the MacBook Pro, connect the portable to the AC / DC adapter, and use the portable. Later, disconnect the MacBook Pro, re-install the battery, and continue to power the portable from the battery - until it fully discharges. Then repeat the recharging cycle.
Clarification:
01. To fully discharge a Lithium ion battery - does not imply 'discharge to 0 volts'; but, to the low battery level of the menu bar or third party application voltage indicator.
02. Others sources to view - ([
1], [
2], and [
3]). Many of [
3]'s web sites state that Lithium ion can be connected more often to it charging system (the AC / DC adapter) with less problems - noted with Nickel Cadmium and / or Nickel Metal Hydride batteries.