I guess it depends on the background. I came from BA so I implicitly know everything the business wants(and still have to break them into phases). I completely

I guess it depends on the background. I came from BA so I implicitly know everything the business wants(and still have to break them into phases). I completely agree with the second paragraph. Sometimes users have no idea what the real data looks like so have to wait. But there are other cases when they see additional data that can be useful if a bit of new data is added, which results in ad hoc requirements.