The main benefit of Matter is that it is split into two layers (Matter and Thread) where as Zigbee is essentially one layer that handles everything. This makes Matter more flexible, since it can work over both Wifi and Thread (and any future protocol at the same layer). At the moment there isn't a huge advantage, but in the future if the standard succeeds, you would hopefully be able to buy most smart devices and use just one protocol (Matter) to control and integrate them.

At the moment, the main advantage I can see is that more wifi smart devices can be locally controlled because they have Matter support (which requires it). Which historically, was limited to HomeKit over WiFi, ESPHome/Tasmota flashed devices, and sometimes through Home Assistant integrations that found a way to locally control devices for a given company.

Because I didn't really explain Thread, I'll just quickly say that it's a protocol much like WiFi and the "closer to the hardware" part of ZigBee. I'd prefer buying Matter over Thread vs Matter over WiFi devices, particularly if you're planning to build out a Thread mesh network (the Matter over wifi devices won't help in that).