Macworld:

If you leave your MacBook, MacBook Pro, or MacBook Air plugged in all the time—no matter the vintage—the battery suffers wear for being charged to full. Over time, the maximum charged capacity diminishes and you lose many minutes—even hours—of usable time. It is just a characteristic of the lithium-ion batteries in laptops and nearly all modern electronics.

Here is a quick list of the best practices for managing your MacBook’s battery.

I have definitely been guilty of leaving my laptop plugged in for days on end.