All plant training techniques are designed to help growers get a more desirable plant shape and bigger yields without changing other aspects of their grow. For example, cannabis plants don't naturally grow in a way that takes full advantage of indoor grow lights - a lot of light is wasted when cannabis plants are allowed to grow naturally without training.
Because of this, cannabis plant training techniques (like topping and fimming) are especially effective at increasing yields in indoor grow setups. Topping and FIMing are very similar to each other in that they create a bushier plant with extra colas, but they do have some differences.