While there isn't a one-size-fits-all sprint length that software development teams should universally adhere to, I think we can all agree that when it comes to sprints, somewhere in the neighborhood of two weeks is the sweet spot. And more than four weeks simply won't do. Here's why:
Small Batches
Since Scrum is an empirical process, the notion of small batch sizes (aka short sprints) is based on the Theory of Constraints, which says that a system is less limited in achieving its goals by a smaller number of constraints. In software, some of these constraints are backlog items (inventory), throughput (velocity), and ROI (customer value).