I added mine after the cab was set, here are my reasons.
With no frame support it is held only by the column clamp, not a great idea so you would have to wire or tie it. It adds another 75 pounds to the lift for no good reason I can see?
After cab is set it will still need to be bolted to the frame, column clamp assembled with correct washers, rubber isolator etc. I Just don't see the advantages anywhere.
https://www.flickr.com/photos/advance-design_parts_co/8129051329/in/set-72157631867396207