The tl;dr version: Smart TV spies on your viewing habits. Well, the incentive for doing this is too great. Such detailed viewing habits can be a minefield for advertisers and marketing companies. Vizio was caught by FTC because it’s too brazen. Others may follow.
According to the original complaint filed by the FTC and New Jersey AG, the company worked with a third party to build smart TVs that could capture “second-by-second” viewing information about what’s on the screen. That includes details on content from cable, internet, set-top boxes, DVD players, over-the-air broadcasts and other streaming devices.
Source: Vizio tracked and sold your TV viewing habits without consent (updated)