As already mentioned you get better visual quality but it won't make a huge difference on a 1080p TV.
In 4K HDR the game looks great (except for the menus which look strange) but 4K HDR comes with a downside. Enabling HDR will give you higher input lag. On newer TV models this is less of a problem, but should you want to upgrade I recommend looking here
http://www.rtings.com/tv/tests/input...comparison_839 before purchasing.
I have the LG E6 TV. Before a firmware upgrade allowed me to enable HDR in game mode, it was unusable for gaming with HDR enabled.