The one great thing of Design Sprints is that it forces user research and product development into a really tight coupled loop. In my personal experience that’s the biggest problem with user research. The amount of information gathered by user researchers is never fully profited in the development process, mainly because they work at a different pace and they were not created to work synchronously. Take Lean UX, Lean Startup and the Design Sprint and you have a process that forces the information you gather into a real tested product.
I understand that — as a design agency — you mostly deal with one-time projects that you need to deliver at a certain date, but what about user research in a project that keeps being developed over time? You keep iterating design sprints?