Hephaestus, our reusable Aerospike engine, will enable single-stage-to-orbit for the launch vehicle it is propelling. This changes the playing field when considering the logistics of a launch:
A single stage eliminates the risk of stage seperation failure as well as second stage engine ignition failure.
For re-usable launch vehicles, it is much cheaper and faster to refurbish a single stage for launch as opposed to multiple stages. Effectively decreasing the turnaround times and costs between launches.