Every time we discuss quantum computers, the headline tends to be that someone, somewhere is going to use the quantum to break your encryption and steal your student loan. If only that were true. But it is probably more realistic to think about quantum computers being used to solve quantum problems. And this has been demonstrated with recent chemistry calculations using a tiny quantum computer.
If solving quantum problems with quantum computers sounds a bit circular, well, it is, but it is also practical. Think of it like this: every protein in your body has the structure it has because of quantum mechanics. And a physicist who is clever, but not intelligent, can write down an exact equation that describes that protein. But not even the most intelligent can solve that equation.
Understanding molecules is hard
A lazier physicist would write a computer script to solve the equation. But that won't work either, because the time it takes to solve an exact description of the molecule will take longer than it takes to go from Big Bang to Heat Death. So we live with approximations. Approximations that are mostly pretty good but sometimes fail spectacularly. And, for some molecules, those approximations don't speed up calculations very much at all.