Nintendo Switch gameplay is "single screen' only
A Nintendo rep has confirmed to Polygon that the Nintendo Switch will be only playable on a single screen be it your TV or on the Switch game pad screen.
“Nintendo Switch is dedicated to deliver a single-screen experience, on whatever screen you might choose"
The Wii U would let you play many games using the gamepad but it seems that's no longer the case on the Nintendo Switch,of course you can still play on the Switch gamepad if someone takes over the TV but you can't play it on the gamepad and TV screen.
For example Mario Kart 8 on the Wii U let's you use the gamepad as a separate map or "horn" while the TV displays your game. The Nintendo Switch unfortunately will require the Screen to be in it's dock meaning you'll have to play withe the Joy-cons or pro controller
