I'm still a Niri newbie, but I'm enjoying the scrolling as a ways to have "subworkspaces": when I'm working on a full-stack project, for example, I can scroll between the backend and the frontend, while arranging my windows in such a way that anything useful (e.g. the browser) remains resident on screen.

You can get similar functionality with tabbed windows, but I'm still trying to decide which workflow I prefer; scrolling feels a bit more "organic", while tabs are superior for density.