Short answer: I think the greatest impacts might be in simulating quantum physics and chemistry themselves, and thereby giving a new window into nature that could have applications to drug design, materials science, batteries, high-temperature superconductors, and more. But I could be as badly wrong as (e.g.) someone speculating about the impacts of classical computers in the 1940s, who could see applications to weather prediction and other physical simulation problems but would've totally missed the creation of Hacker News.

Long answer: See my recent blog post https://www.scottaaronson.com/blog/?p=3848 about exactly this!