If you live in Google Photos, then this makes sense for quickly sharing photos between you and your close friends and family. Your message history will stay there just as it does in chat apps, but the advantage here is the simplicity of keeping all your media and shared media within the Photos app itself.
The service supports group chats. You can set up a chat by selecting images or videos and tapping Share, where you can then ‘Send in Google Photos’ from the share sheet – see the below GIF.
It looks like it’ll massively simplify sharing photos, particularly for Android users. Why this hasn’t been a thing before is baffling, but Google does love to launch, and then kill, chat apps. Perhaps the company has taken a step back and realised all it needed to do was add messaging capabilities to one of its most used apps rather than trying to create one from scratch.