Not really ... increased power consumption if you leave both screens on?
When I used my laptop, I always had it hooked to a screen at home, as do a lot of people I know. In fact there are a lot of advantages to hooking your laptop up to a monitor (and possibly keyboard/mouse too). Increased viewing space, less wear on laptop screen. Plus the keyboard/mouse gives you greater control and more ergonomic typing. Frankly the only time I wouldn't have mine set up that way would be if I were on the couch or out of the house/office.