Some clients like to remove their MacBook or MacBook Pro battery when they are using their power adapter for a long time. The theory is that this will conserve their battery life.
Apple don’t like this idea:

If the battery is removed from a MacBook or MacBook Pro, the computer will automatically reduce the processor speed. This prevents the computer from shutting down if it demands more power than the A/C adaptor alone can provide.

Of course, if you bump the power adapter and unplug your laptop, you will lose all unsaved work. Not to mention that if dirt and dust collects on the battery connectors you may have problems later.

There’s an Apple article here explaining how to calibrate your battery - this should be done every couple of months.

Sounds kinda annoying to me, so I’m going to buy a second battery and one of Newertech’s battery charger and reconditioner units - gotta keep the MacBook Pro on 24/7….