Since the release of the Game Boy in 1989, there has been a pretty fundamental split between playing games on a TV-based console and playing games on a portable system. Aside from pricey experiments like the Turbo Express, playing on the go meant making significant and understandable sacrifices in graphical and computational power (and, often, controls) compared to contemporary home consoles.
With the Switch, Nintendo seems to be betting that the continued drum beat of Moore's Law and miniaturization has made that dichotomy moot. The Switch is an attempt to drag the portable gaming market kicking and screaming to a point where it's literally indistinguishable from the experience you'd get playing on a 1080p HDTV. Nintendo is betting that a system that fits in a diminutive tablet form factor is now powerful enough to feel acceptably modern when you throw it into an included dock and blow it up to full size on your living room wall.