Current spacecraft achieve a change in velocity by the expulsion of propellant, the extraction of momentum from stellar radiation pressure or the stellar wind or the utilisation of a gravity assist ("slingshot") from a planet or moon.
Even ignoring for the moment the impact on interstellar travel, future spacecraft driven by impulse engines based on Mach effects would represent an astounding breakthrough in terms of interplanetary spaceflight alone, enabling the rapid colonization of the entire solar system.