When the requirements are agreed upon and the technology is well understood (good examples of this categories are building a house or a bridge) the project falls under ‘Simple’ region in the Stacey’s matrix (see the picture below). In these scenarios waterfall approach will work just fine.
However, in reality most of the projects fall under ‘complicated’ or ‘Complex’ region. In these cases, rather than laying out elaborate plans that you know will change, it is often better that you create a more fluid options. Try a little, inspect the results, and adapt the next steps based on the lessons learnt in previous cycles (sprints). Indeed, this is exactly what’s known as the empirical process model.