Just speculating, but firmware updates might be useful. Some display resolutions, refresh rates, VRR, etc might not have been programmed correctly and later fixed. They could add new features like offsetting pixels slightly differently over time to reduce colour burn in or something that might reduce warranty claims (I don't really expect them to add more value to the TV through new features unless it would help them financially).

That said, I've never connected my current TV to the internet and it's been fine. I'd suggest trying an update if your TV does something annoying or isn't working as well as you'd like. You can also read about your model online to see if there are any updates available and what they do to determine if you want them.