Creating Realtime Chat - Reasons for using external API service (e.g. Ably) vs Xano database

Hello,

I'm looking to build a chat functionality in my app. I've watched the Xano videos on Ably Realtime Chats (Ably Realtime Chat Template - YouTube) and it seems to me that you can read/write chat records directly to the Xano database without really needing to go through Ably. There's a gap between getting the ably API response (which is only a channel_Id and message_Id) and integrating the realtime chat app to the frontend.

For example, when messages are passed into the Ably API, the response from Ably is just a channelId and a messageId but then all the inputs in the Xano API (chatroom_id and message) are added directly into a Xano db table after the Ably API call and I don't see the response from the Ably API (channelId and messageId) being used at all.

So I'm curious to know if there are particular advantages of / reasons for using Ably for a realtime chat app backend in Xano over simply using CRUD functions to add data directly to the relevant Xano tables. I'm aware Ably could be used for push notifications which Xano cannot do but as far as realtime chats are concerned, what would be the benefit of using a third-party service like Ably over using CRUD actions to read/write from the Xano db?

Just trying to understand what part of the big picture I'm missing.