Difference between group messaging and private category?

After 1.5 year using discourse, I am puzzled regarding the difference between a private category that would be accessible/visible to only one group, and group messaging within that same group. Is there any?

Typically, for a group that want to discuss their private project, the PM board of that group list all topic titles very much like a category does and I find little advantage to creating a private category. So am I overcomplicating things if a private category is created only for one group?

The main difference is how the messages are displayed. In a category, everyone with permissions has visibility of every topic in the feed. PMs would be mixed up amongst an individual’s other PMs (if they had some).

That the PMs would be mixed amongst other messages, isn’t this also presented per group, avoiding the confusion you describe, like in my screenshot (mobile version):

Yup, it absolutely is – it’s just a little less visible/intuitive if you don’t know what you’re looking for.