I notice that my macbook pro stays "warm" when plugged into my screen, even if it's closed. I think it might have something to do with powering the USB or displ

I notice that my macbook pro stays "warm" when plugged into my screen, even if it's closed. I think it might have something to do with powering the USB or displayport connected devices. I now unplug my computer when I'm done, which is kind of annoying.