If something like this is not invented (or if it just impossible in the first place), we are simply stuck with very dangerous, long-term space journeys within our own little corner of the solar system only.
There will be no 3 year journeys to Jupiter or 10 year journeys to Pluto or 100,000 year journeys to the next star.
So we might as well try out some of this exotic stuff and see if any of it pans out.
one hell of a right turn getting past the asteroid belt