Perhaps this is something that would have to be implemented by Xfce rather than Linux Mint, but it would be good if keyboard shortcuts could be added to Xfce to move the active window to the next monitor in a multiple-monitor setup. This could either be "move to next monitor" or "move to monitor 0", "move to monitor 1", "move to monitor 2", etc.
I use a triple-monitor setup and really like Mint Xfce. However, I so frequently need to use keyboard shortcuts to move windows from one monitor to another that I had to switch to Mint KDE to accomplish this. I would actually prefer to use Mint Xfce because of its elegant simplicity and greater stability compared to KDE.