If you do a dry run, moving a computer to a different data centre, and it works, why would you move it back?
If that still doesn't make sense, think back to the days when moving a computer included a physical activity: unplugging the computer, putting it on a truck, and shipping it to your new data centre. Would you really propose that you do a dry run of that, then, if your dry run succeeds, putting it back on a truck, moving it back to the old data centre, getting it running again, only to then do it "for real" some time later?
Granted, in the world of virtual computers, you don't have to actually move the computer back. However, there is still a list of activities you have to do to move a virtual computer, that you have to undo. There's just as much a chance you'll screw up the undoing of those steps, as there is that you'll screw up the doing of them in the first place. A dry run actually increases the overall risk of the relocation.