In addition to being combustible, Tritranium has the unique property that allows it to be compressed without exploding. As such, when machines receive the compressed form of Tritranium as fuel, they will be able to run for days without the need to refuel.
Tritranium was used by Dr. Robotnik as a fuel unit for his Sleepers. Eventually, however, he ran out of Tritranium and had to go to the Badland Mines (the only know source of Tritranium) in order to find more. Upon uncovering a vein of said Tritranium however, the Sonic Underground destroyed his reserves in order to prevent him from making more Sleepers.