There’s a new protocol for smart home devices called Matter, that let’s them work across ecosystems (so for example smart lights set up with Google Home could be controlled through Apple HomeKit via Matter). Thread is part of how Matter devices communicate with each other (instead of e.g. WiFi or Bluetooth). The new iPhones can directly use Thread instead of needing another devices to act as a bridge to “translate” the commands
A fairly niche addition, but definitely not useless. And a big plus for those into smart home stuff