Slack is what you make of it.
When we were a small organization, it was a great tool. As our organization's grown - and added people with different work- and conversational-styles (and, perhaps more-crucially, people with differing ideas of netiquette), it's become less helpful. I've pretty much de-subscribed from any channels I don't absolutely need to be a member of. The ones that I don't need to actively monitor, I mute (that way people can still pull me into a conversation by @-mentioning me).
A lot more useful in this dialed-back configuration.
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