These changes apply whether you noticed or not
A new fee in a marketplace's seller terms. A changed clause in a supplier agreement. An updated rule on a government page. They usually take effect on a set date, and nobody emails you about them.
A dated record of every change
Each change is stored with the date we spotted it and the exact wording before and after. It's not a legal archive, but it's very handy when someone asks “when did they change that?”