My attempt: ambiant temperature superconductor would be like when we went from lamps to semi-conductor. We were doing many things already with lamps, but semi-conductor allowed for incredible miniaturisation and efficiency. They allowed the invention of computers, Internet and smartphones.

We already do many things with magnetic fields, but ambiant temperature superconductor would be a big technologic jump.

Many things would rapidly become much more efficient, but we have no idea yet of the full potential of this technology. It could be helpful for quantum technologies and fusion reactors for example.