As others have already mentioned, spaceflight has useful applications at creating a long term stable population center outside of Earth. There's also the commercial application of being able to gather vast resources relatively cheaply from the asteroid belts once there's a platform to routinely and cheaply transfer cargo up to space, down is relatively easy. We're going to run out of raw resources at some point and this will be the least costly application. Deep well drilling could access large amounts of trapped resources however the cost is prohibitive for the return.