Used properly, a design sprint is a fast way to get answers. We run them on the problems our discovery work uncovers, and come out with a tested prototype that can go straight into build.
Where client teams can commit the time, we run a full sprint on every key objective we find. Where schedules will not stretch that far, we still apply the method internally, so we are never just working through a list of scope. Every problem gets solved on its own terms.
We use them when they fit, and only then. A sprint is not our only process, and some work is better done another way.
A typical sprint runs to 5 key steps over 5 days, though it stretches or shortens to suit the problem being solved.