It depends. Group DMs/chats make sense when the nature of the discussion or topic is more private in nature, like a close group of friends/family, a business or hobby project group, etc. But it doesn’t make much sense to me to have a large general purpose chat. Except I guess it could provide redundancy of connections, like if you lost access to your Nostr account then you could message people on that other chat and they’d know it’s you. That’s about the only benefit I see.