The relative effort estimation seems to be more-or-less accurate for small chunks. However, at the beginning of a project, you don't know how many small chunks

The relative effort estimation seems to be more-or-less accurate for small chunks. However, at the beginning of a project, you don't know how many small chunks there are. In a small project, you can reasonably plan and estimate most of the chunks ahead of time and (eventually) plot out on a burn down chart that shows roughly when the project will complete. However, in a large project, you can really only plan the beginning of the project this way. Eventually there are too many unknowns and you risk all the downsides of waterfall design. In my experience, a project like this has a burn down chart that goes UP over time (i.e. chunks are added faster than they are completed). This makes estimating the project impossible, especially if the chart is still concave-up (i.e. the rate at which it increases is increasing). If you estimate large chunks, then you are less likely to add them over time, but you also won't be as good at estimating them. I think this is a good method for determining if a project is closer to a 1 year project or a 10 year project though. E.g. if you have 10 large equal chunks in a project and it ends up taking you 6 months to complete the first 1, you probably aren't going to finish by the end of the year, and you should evaluate if you are happy spending 5 years on it before you spend any more time.