Your "Scan History" graph not only lets you keep track of the issues on your site, your score, and the fixes you have made to date, but it also serves as a useful tool if you are ever targeted by a web accessibility lawsuit.
Websites that are able to prove they are taking active steps towards making their website compliant are far less likely to be subject to fines and penalties. However, this will differ on a case-by-case basis, and you should always consult with a legal professional before making any assumptions.
