All of the transportation needs in space –— from orbit raises to station keeping to Lunar landings or even expeditions to the outer planets –— are near infinitely more achievable when access is fueled by the resources present in near-infinite quantities on asteroids.
In short, harnessing the resources of space for utilization in space is a far less daunting challenge than we are prone to believe.
To help visualize why asteroids play such a vital role and where Planetary Resources comes in, they have produced an educational short for you.
Prospecting and staking claim on asteroids will drive economic growth into the Solar System.