Slack is primarily used for communication, file sharing, and sometimes for Huddle, which is similar to a Zoom call within Slack. You can start a call with the person directly.
Slack offers several valuable features. Firstly, they have a message deletion feature, which is now available in other software as well, but Slack was the one who introduced it in enterprise solutions.
Additionally, Slack has a great feature for creating communities. This means that if you want to communicate with someone from a different company, you can create a channel specifically for them. They won't have access to other channels or public channels in your company, only the channel you've created for them. This is particularly useful for our interactions with one of our client, as we have a dedicated channel with them, allowing us to receive support. It's one of the best use cases I've seen for Slack, apart from its primary use for intra-company communication.