Given the current state of quantum technology, it will be useful sooner for small-scale problems whose solutions offer smaller benefits and will only later be viable for solving more complex problems that promise larger benefits.
Benefits will come on a continuum. Quantum computing becomes more attractive when the quantum algorithm is exponentially faster or significantly better than the classical computing option, or if the problem size being tackled is larger than the speed differential between the two. Given the current state of quantum technology, it will be useful sooner for small-scale problems whose solutions offer smaller benefits and will only later be viable for solving more complex problems that promise larger benefits.