I believe he meant sessions being portable across devices. You cannot start a X application on your laptop, disconnect, switch to your desktop, continue using t

I believe he meant sessions being portable across devices. You cannot start a X application on your laptop, disconnect, switch to your desktop, continue using the application. (At least, it does not easily work out of the box. Allegedly it is possible in certain scenarios.) VNC and other on-top approaches can do this (even with Wayland).