Remember way back when Apple used to put power buttons on their keyboards? Then they removed them and someone made an excuse that it was because they couldn't turn the computer on via USB? Well, that's not true. My old style iMac G3 pre-Pro keyboard still works fine with powering on my Macs. At least the PPC ones. Does it still work with newer Intel ones?
Frankly, I prefer to use both monitors when connecting one to my MacBook. I get more space to work with that way. My 13" built-in and my 20" Apple Cinnamon Display.