If I modify the price at 07.20 and you modify the from date at 07.22 you are the last modified user Sometimes it is important to know the change made as well as the person. Arguably slightly different with Trade Agreements as they are journal based, but the concept is still the same.
And that is why you would activate the database log that gives you the value of the record before, after, user, time etc. But you said modified by was enough [;)]