[GeeTwo]

Another advantage of Slack over E-Mail chains:

As to something much lighter-weight than an e-mail response, on our team slack account we make extensive use of the "add reaction" action. For example, if we are in doubt as to attendance at an event, we'll ask those who will be there to "+1" or "-1" the post as to whether or not they will attend. Slack then automatically provides counts, and hovering over the thumbs up (+1) symbol tells us who agreed to show up very quickly.

The main advantage, of course, is that team members can decide dynamically whether or not to join a channel, and once the member joins, [s]he can see the whole post history. This is just plain not feasible for "long e-mail post" discussions.