Group chats are quick to make, refresh to the top, and naturally expire. It's nice that chats can be renamed to focus on a topic.
You'll have to use channels. Channels enable connectors like webhooks*, and it's the only way to speak to folks outside being invited to chats.
* Webhooks will be deprecated in a few months in favor of Power Automate.
I guess channels and chats differ by exclusivity and recency. Chats auto-sort by latest and are invite-only; a Team can be a "public square" for petitions or callouts.
There are use-cases for private Teams if additional features beyond chat are needed.
Channels require scrolling, so it's usually easier to ping someone instead. Channels as webhook sinks incentivize regular checking, but only if the user is actively seeking.