Mostly bug fixes relevant to higher end home theatre setups. Typically bleeding edge stuff where a TV is released before a new HDMI spec is fully baked or whatnot. One of my older OLED panels needed a number of updates to get proper Dolby Vision profile support a few years back.

Typically not all that relevant most of the time to the average consumer, but if you’re having a persistent annoyance it’s worth looking through release notes from time to time.

This ignores that the vast majority of consumers actually use the smart tv features like the Netflix app. Then updates start to become far more relevant and eventually mandatory.