I've been using Duet app intensively lately. The app lets me to use my old iPad 4 as the external monitor for daily use. Is it ok to keep the iPad plugged into the MacBook Pro all the time?. Will it add any new kind of stress to MacBook Pro?
Actually, frequent charging habit is good for the Lithium-ion battery use device.
You could refer this Apple official page. http://www.apple.com/batteries/why-lithium-ion/