I always wonder why the default for a desktop is to have various ttys, but only one X session running. I always find it useful to have various X sessions, guarded by various xdm. That way, I can have my normal tiling window manager for normal work, and simultaneously have a more graphical window manager for image editing. Additionally a graphical session for the different Unix user that handles my VMs. And a session of the guest user for visiting friends who quickly wants to check their emails. Etc, etc.
Therefore, my /usr/local/lib/X11/xdm/Xservers looks as follows.
# # Xservers file, workstation prototype # # This file should contain an entry to start the server on the # local display; if you have more than one display (not screen), # you can add entries to the list (one per line). If you also # have some X terminals connected which do not support XDMCP, # you can add them here as well. Each X terminal line should # look like: # XTerminalName:0 foreign # :0 local /usr/local/bin/X :0 tty8 :1 local /usr/local/bin/X :1 tty9 :2 local /usr/local/bin/X :2 tty10 :3 local /usr/local/bin/X :3 tty11