Quantum computers are (conjectured to) outperform classical computers in a very restricted set of problems. These problems happen to be extremely important (e.g. protein folding and some forms of linear algebra), but for tasks that are already efficiently solved by classical computers you probably will never use a quantum computer (maybe in many decades this will change, when it becomes as "trivial" to construct quantum CPUs as it is to construct classical CPUs)

Or the subset of users who need what a quantum computer can offer add something analogous to a GPU to their general purpose computer.