On a group chat, the responsiveness is critical. You want the users to feel that other people are either reading them or typing a new message. You want to show activity.
12 tips for designing a better group chat experience
Max Masure

This in an important feature to messaging that I think people undervalue because it seems like such a little thing. I think this goes for both group as well as 1:1 messaging.

Personally I find myself waiting for a little after I text someone to see if the bubble pops up to show that they’re responding. (referring to iMessages)

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