More customers being able to be served from the same number of towers with better per-customer performance.

One challenge in rural broadband deployments is there are only so many good locations for the carrier to actually stick antennas. Maybe a water tower or two, you might get lucky and have some tall radio tower at the edge of town. So then all the customers in the area are essentially sharing a single tower, all needing to point their CPE to that one point. You can only slice the tower up into some number of sectors and once you hit that point the tower is saturated. Every additional customer is now diminishing the service for every other customer.

Having better spectral efficiency per sector means you can service more customers, have better service per customer, or even both depending on how you balance it.