It depends on the voltage the battery is charged to, so a twiddler engineer should be able to best answer this question...
If the charger stops charging at ~3.7-4.0v, then I'd say it doesn't really matter whether you cycle it normally or leave it plugged in. However, if it charges the battery to the brim (4.2v) then leaving it plugged in all the time will be very detrimental to the battery's longevity.
Also, something else to consider is the strain that will be put on the micro-usb port when it's connected while you use the device.