I think they aren't referring to "where does it go?" and more being forgetful.

If you have something that would be reasonable to open on any workspace because it's ephemeral (they used a tmp terminal as an example), and you open it, navigate away from it, and then switch workspaces a few time, and then get pulled into a meeting or go to lunch, and come back, switch workspaces a few more times...

"Where did I leave that terminal, I dont remember where I was when I opened it."

In i3wm/sway etc, you can cycle all your workspaces and eventually one of them will have it visible. On Niri, as you cycle through all your workspaces you may never see it because you don't see all the windows in a workspace, unless you scroll through the workspace panes as you cycle workspaces.

It's not a problem necessarily, but it is something to consider. It sounds like this doesn't affect your workflow, but it might affect others.