it's always advisable & in good care to take out your battery if you're using your laptop while it's plugged-in to a power source for a long period of time. from my own experience, there'll be a deterioration of your battery's health, which i observed using CoconutBattery, back when i was being careless with my macbook pro. initially with a 100% charge, it'll last about 4 - 4.5 hours. now it's more like 3 hours.

so don't be lazy guys do what's best for your mac.