Tanks are very heavy and they cannot rest on rubber tires. We could use steel tires. But the small area of contact between the ground and the tires creates a high stress (pressure) on the ground. Then soft or Earthen ground or loose roads will sink. It affects the mobility of tanks which move at 40 kmph or more.
Hence a steel chain is used. It is called continuous track or caterpillar track system. The chain or band is made of modular steel plates. These allow distribution of the weight over a very large area. So tanks move continuously with out problems.
These metal plates help movement of tanks in any kind of terrain with uneven surface. It can climb heights, abrupt steps which is very difficult for tires or steel wheels. It gives grater control for turning, slowing or speeding up in deserts, among mountains, on damp lands, on roads etc.
Further when missiles are fired, the recoil force is transmitted to the ground. Hence, the continuous track helps in distribution of force over large area.