Lithium batteries do not like to be at 100% all the time. Their happy zone is between 20-80%.
My wife and I have owned MacBooks for the last 15 years and I use mine as they are intended: I use them on battery and then charge when getting low. My wife leaves hers plugged in all the time. The last 3 macbooks she’s had all had battery issues within a few years while mine are still going great. My oldest machine a 2012 Macbook Pro 15 retina, still has 88% after 8 years and 500+ cycles.
My wife’s 2015 MacBook 12 has only 70 or so cycles and is down to 65%. Her last macbook’s battery also crapped out early. There’s a reason why Tesla allows you to purposely limit charge percentage on their cars to extend battery life. I stop mine from charging above 80% as my commute is only 30 miles.
Newer MacBooks may have better battery protection built in, but Apple’s beta MacOS has a new optimized battery charging setting to reduce battery aging that was copied over from iOS...
You should plug it in as much as possible. Keeping the battery topped off reduces charge cycles and extends the overall life of the battery. Lithium ion batteries do not have a memory like the old nicad batteries. Charging as often as possible is the best way to keep your battery healthy.
It's been known for a long time. It's the same reason that it is recommended you plug in your laptop if you can. Just run the battery down at least once a month and you'll be fine. It's way better to plug in and use a charge cycle every 3 days than to use 1.5 cycles every day.
You can read about all kinds of stuff here:
http://batteryuniversity.com/learn/article/how_to_charge_when_to_charge_table
When draining the battery all the way down and recharging it you are not recalibrating anything on the battery itself. It may help a little for the battery percentage in the software to be slightly more accurate but again the battery has no memory whatsoever. It is not possible to "recalibrate" the battery itself. The more you drain it low the more charge cycles you will incur and the less life you will get out of it.
This applies to all lithium ion powered devices. I always top off my batteries when possible, like driving in the car, and I see excellent life compared to many others because of this habit.
Yes, it’s better to use portable Macs off of the main supply (use the laptop battery). From time to time, (as it helps to keep the battery “healthy”), run the MBP off the mains supply (use battery) until the battery percentage reads around 80% and recharge. Once or twice a month is enough.