Most general purpose computing is based on algorithms that are essentially O(n). What that means is that they are a constant times the cost of simply reading t

Most general purpose computing is based on algorithms that are essentially O(n). What that means is that they are a constant times the cost of simply reading the input. Often, the computation is actually cheaper. Quantum computing might make some computations have a smaller theoretical constant, but it is almost certain that the practical constant ($/bit of input) will be much, much worse due to scale. Right now, only very specialized computations look like they will ever have any speedup. And even that is only maybe, in practice.