Aside from the obvious benefits that a future amputee victim might experience, the implants could also curb tremors, manage pain or treat spinal cord injuries—just to name a few.
Beyond that, DARPA (and SMU) has once again has found a way to blend the present with what was once science fiction:
"Science fiction writers have long imagined the day when the understanding and intuition of the human brain could be enhanced by the lightning speed of computing technologies. With this remarkable research initiative, we are truly beginning a journey into the future that will provide immeasurable benefits to humanity." - Dean Osark, SMU Lyle School of Engineering.