At AgileBits we are using both Workplace and Slack. While nothing could be Slack for real-time chat, Workplace is much better suited for announcements and discussions that could span several days and even weeks. It helps that comments are threaded and it is possible to reply to a specific comment instead of the entire post.
There are a few features that could use more work. For example, it is not that easy to format posts and if you forgot to specify that you were using Markdown then the entire post has to be recreated. Also, it is not possible to use Markdown formatting in the comments.
The timeline still confuses most of us. It is not clear why some post appear and some posts do not appear on the timeline. There are just too many smarts, it would be more effective if timeline was always chronological and included all posts from the groups I follow. I ended up using just the notification popup to keep track of the new posts and comments, which is not ideal.
We use different groups to communicate within teams. We also have a single Announcement group for company-wide announcements.
Most of our company is remote and in many different timezones. Workplace helps us to communicate asynchronously — some of the discussions take place over several weeks.