Zeit (the company behind `now`) recently killed their 10,000+ member Slack server in favor of Spectrum. Their reasons were (a) Slack isn't designed to support communities, (b) they were having to answer the same questions repeatedly, (c) those answers weren't being indexed by Google, and (d) there is very little abuse prevention in Slack.
Another way of phrasing (d) is that they seemed to want to have greater control in shutting down conversations (for better or worse).
Lopping the head off a 10,000 member community seems like a bad idea, and that was only reinforced by the outcome. People regularly complain about Spectrum on Zeit's spectrum. Threads go unanswered, sometimes for weeks. And every conversation is forced into a threaded model. There's no way to have a single, shared chatroom that everyone is posting to. (Or if there is, it's not the default, and defaults matter.)
The nice thing about Zeit's old Slack channel was that if you were facing a crisis with `now`, you could post in #now and their support staff would take care of the problem almost immediately. But more than that, you could see that other people's problems were being taken care of immediately. That strengthened my brand perception of Zeit and made me want to recommend `now`.
I still recommend `now`, but losing out on real-time support felt like a major blow. When my payment details lapsed, all of my `now` deployments were shut off immediately. I updated my payment details, but the deployments were still offline. I felt somewhat foolish posting a Spectrum thread like "Hey, I know I was supposed to be paying you, but I didn't. Now I did. Will my deployments come back online, or do I have to re-deploy everything?"
I didn't want a conversation like that to be indexed in Google for all time, public for all to see. And while there may be a DM feature in Spectrum, the benefit of Slack is that you can get a sense of who's who right away. It's obvious who the support person is, because they are the ones fielding everyone's questions each day. And you can just shoot them a quick message for one-off questions.
No doubt that gets annoying. But from an outsider's perspective, it's hard to understand why the trade-offs are worth it.
Meanwhile, Discord seems to be gaining traction in the developer space. There are a lot of interesting programming communities springing up, like The Coding Den. Many open source projects are starting to offer a Discord presence by default. And there are a lot of benefits with this model: All the upsides of Slack (and then some), minus some Slack integrations that you might miss (which you can use Slack for anyway), and without forcing every conversation into a threaded async model.
All of that said, please note that this comment is written as an outsider's perspective with relatively little Spectrum experience. Maybe I'm just using Spectrum wrong. But the benefit of the Slack/Discord model is that you end up feeling like a community, rather than a disparate set of posts that are basically tweets.