The lower you are in the spectrum band, the more propagation you will be able to have.
Propagation has two dimensions. One, it will go further, so with one tower you will reach a greater distance. Secondly, it will permit you to have cellphone conversations if you're in the third basement of a garage. So it has propagation both horizontally and vertically, if you wish.
For a carrier, it means that their deployment will be less costly. Instead of having to build five towers and link them all, they can build one tower. It reduces both the cost and the community heartache associated with putting up towers.