Pretty much any ODE solver you want double. All of CFD (fluid sims) and FEM (mechanics) use double. It can also be a big help in graphics. Basically, if you're doing fine meshing, doubles will help you. There's a balance between your meshing size as well. Your life is a whole lot easier and you'll get better answers if you just use double. Ask literally any computational {physicist,scientist,engineer}. We've all tried without double. Trust me, I'd love to have lower memory constraints.