Security vulnerabilities. Performance increases. All the devices that were vulnerable to Heartbleed (as an example) with no ability to update themselves are still vulnerable. One could argue that simply disconnecting the device would be sufficient, but this ignores the possibility of internet features being useful; I wasn't limiting the discussion to TVs.
But it's a useful exercise to limit the discussion to TVs exactly because most TVs don't need any Internet connectivity at all! They just need to display input from other devices that are connected to the Internet.
The trend for Smart TVs these days is to leak data like a sieve. The small risk of vulnerabilities in e.g. a TV's HDMI layer being exploited is arguably a price worth paying for privacy.
I recently bought a Panasonic TV that doesn't have smart TV features - the pictures as good as the smart variants, it has a couple of HDML ports and no network interfaces.
The discussions around smart TV vulnerabilities is making me very pleased about that decision.
