This is the same reason people use cavalettis and other training tools- building on muscle memory so that they can be more agile in the future. (Think flyball- not hitting the box SO HARD.)
A lot of bigger dogs aren't sure how to control their back legs from the rest of their body- and in agility, and other sports, it is crucial for the well being of the dog.
This isn't hard to train at all, and it's VERY beneficial in the long run. So get training today!