We have implemented cumulative flow diagram in TargetProcess v 2.15 as a tracking/reporting chart to get a quick overview of user stories in To Do, In Progress and Completed state:
Why we have only 3 fixed states for cumulative flow diagram while all the states for User Stories and other entities are customizable? We could have enabled showing the count of User Stories in all the customized states, be it 6 or 7 or 8 states. But the visual diagram would have been too clogged this way. We would have had to either follow the reporting stats meticulously, replicate all the states and counts in the digram and lose the visual UX of this chart, or to get it down to 3 basic states such as ToDo, InProgress and Completed (all the customized states are just a variation for those 3 states, one way or another) and retain a good info-design.
Some people asked us to enable more detailed views in cumulative flow digram and we will consider implementing this in the future.