Computerized simulation is used in a variety of applications, such as how to design the most efficient intersection, how diseases spread, or how the climate changes. However, some systems cannot be efficiently simulated on classical computers. One example of this is the interaction and reaction of molecules: chemistry. Simulating chemistry might be useful in material development or medicine development.
The model for chemistry simulation is the Hamiltonian, a large matrix. Plugging it into a classical computer scales exponentially, whereas a quantum computer scales cubically. However, two caveats exist: only certain properties can be simulated efficiently, and the quality of the output depends on the quality of the input.
There a probably other things that can be simulated more efficiently using a quantum computer, apart from chemistry. Can you think of a few?