This incredibly innovative and futuristic system is part of Radically Enhanced Mobility portion of the GXV-T program. DARPA describes it and the tracks in a press release , stating:

Wheels permit fast travel on hard surfaces while tracks perform better on soft surfaces. A team from Carnegie Mellon University National Robotics Engineering Center (CMU NREC) demonstrated shape-shifting wheel-track mechanisms that transition from a round wheel to a triangular track and back again while the vehicle is on the move, for instant improvements to tactical mobility and maneuverability on diverse terrains.

Radically Enhanced Mobility: GXV-T envisions future combat vehicles that could traverse up to 95 percent of off-road terrain, including slopes and various elevations. Capabilities include revolutionary wheel-to-track and suspension technologies that would enable access and faster travel both on- and off-road, compared to existing ground vehicles.

Such a capability could be downright revolutionary if it were to make it to an operational state. But just because it works for a technological demonstration, doesn't mean it is anywhere near being ready for combat operations. Cost, complexity, and durability are all key questions that would have to be answered if the system were to make it into production.

But even if those hurdles remain somewhat steep, such a capability could be worth the headaches they may cause in an operational state for certain users. The USMC in particular, which focuses on executing transitional fights from the beach to inland locales, could make great use of this technology on Humvees and Joint Light Tactical Vehicles (JLTVs). Even larger armored personnel carriers could leverage a form of the technology.

Equipping scout/reconnaissance and special operations vehicles with such a system also makes some sense as they may venture where road conditions are unknown, and with little fire support for protection. Being able to morph between wheels and tracks at an instant, and thus offering high-speed and rugged terrain access flexibility, could literally mean the difference between life and death.