Many northern Canadian communities lack road access. Hundreds of kilometers of swamp, tundra, or muskeg separate the communities from the nearest highway. They have to wait until winter freezes the mud into a solid mass, so they can bring in supplies in trucks driven across temporary ice roads.
Continuous tracks are a useful way for vehicles to get around swampy, muddy, snowy, and rough terrain. Instead of wheels getting stuck in the ground, a vehicle's weight is spread across a rubber or metal track. The maximum weight of the vehicle on any given terrain is proportional to the width of this track.
If you have a wide track, you need a long unsupported axle. Long axles tend to break when driving across rough terrain, especially when you have a wide, heavy track bouncing around as unsprung weight.
What if you could make the track wide where it contacts the ground, but still have a narrow track that fits snugly against the side of the vehicle?
We could add hinged flaps to the treads (green in the attached sketch). When the treads are on the ground, the flaps are extended, tripling the width of the track and dropping the ground pressure. As the tread moves upwards, an idler wheel pushes the flaps inwards. When the tread starts moving down to contact the ground again, another idler wheel spreads the flaps apart again.
Moving parts wear out quickly and jam, especially in a muddy environment. We'd need to make the hinge pins deliberately weak. If a flap got caught on something, or grit kept it from folding back neatly, the hinge pin would shear off before the rest of the track would be damaged. On a long trip through a swamp, you'd leave a trail of ripped-off flaps behind you. On your return trip, you'd have to count on the reduced track area being counterbalanced by the reduction in vehicle weight.
Anyway, that was my idle thought for the day.