You can see your company's Slack stats here https://[your-company].slack.com/admin/stats For example at work we noticed a high number of DMs (> 80%) and we're trying different things to bring that number down to promote more transparency, collaboration, and opportunity to impact decisions across the team.

Department-channels (#backend, #web, #ios) can get pretty chaotic with multiple threads getting discussed concurrently. I can see how a topic-channel (#android-release-process) would help you swarm more efficiently. But, making it private and inviting only those you think should be there seems counter to the goal of transparency and "swarming". Maybe you could originate these topic-channels from a general channel with "@group, we're swarming on #android-release-process" and make it public.