We've seen plenty of video of what happens to a quad motor when a couple of wheels are off the ground - effectively asking the remaining motor or two to supply all the power needed.
It seems to me that this method would suffer from a similar condition when a single motor is asked to supply all the power/traction.
It would be worth testing under various conditions. It might be more useful in some conditions than others where more "help" is needed.
You would put it on the wheel that is in the air or spinning, since then it could help move the vehicle forward. A more basic method is looping a strap through the wheel, but trickier to keep the strap aligned with the tire, and you need enough clearance from the wheel to the brakes.
Here's a video showing the technique.