It can be useful if they build enough of these that they can run programs that regular computers can’t run at this scale, in less than an hour.
Quantum computers aren’t a replacement for regular computers because they’re much slower and can’t do normal calculations, but they can do the type of problem where you have to guess-and-check too many answers to be feasible with regular computers in many fewer steps.
You think that’s wasteful? Wait until you hear about the military or prisons.