How many % of the requirements are necessary and used?

In mostly every agile training people are shown the results of Chaos Report of The Standish Group which shows how many % of requirements are/are not used.

Chaos Report – The Standish Group

These numbers are very important for agile teams. It is proof that big requirements upfront (BUF) makes no sense. In case of constant changes, there is no other option than continuously consider requirements, evaluate their business impact, risk and cost and develop them iteratively. See more details in this article.