Also, I find feature-specific channels to be such a pleasure. It's easy to have everyone focused on the same topic in a given channel, without any confusion or missing information between different channels or private messages.
Moreover, I have also considered Slack to be asynchronous - meetings are necessary for sync work, but I find Slack to be working perfectly if no one expects that you reply within minutes, but within a few days (if you are not actively working on a project - in that case a lot of times is just easier to schedule very fast meetings during no-focus times)