The desktop clients are ridiculously heavy weight indeed, since most of these chat clients are built on top of Electron. However most of them also provide a web interface that can just be loaded in a browser, which reduces the memory usage to more acceptable levels. I’ve set up Whatsapp, Discord and Slack like this as pinned tabs in Firefox and according to the task manager of Firefox they now use 35, 75 and 110 MB of RAM respectively.
In the current environment where I’m involved, it’s used for team collaboration among a team that works together on 2 projects with a common base. Multiple channels have been created for subtopics within the projects and the common base, so that discussion per channel can be focused on 1 topic. Still it happens frequently that discussions end up quite chaotic and people end up using 1-on-1 chat (which is not public) to discuss more final details. Of course this also depends on the users, but just want to bring this into the discussion.
On another note: before using Slack and Discord we’ve been using Mattermost and personally I liked it better than both Discord and Slack. It’s very similar to Slack in user experience, has native clients for Windows/Linux/Mac/Android/iOS, supports audio/video, sharing code snippets etc. and is open source. It can be self-hosted, but they can also do the hosting and have specific pricing for open source projects.