Just now I submitted an edit to an answer that only needed some extra command-line options. But I couldn't submit it as intended because it only added up to 4 characters changed, and the requirement (at least for my reputation) is 6.
In this particular instance I was able to add some dummy command-line options (that don't do anything) to get to 6 characters, but that isn't always possible and it's certainly not ideal from a readability standpoint. Furthermore, typos that would otherwise be worth correcting are often not more than 6 characters.
Removing (or at least reducing) the minimum number of changed characters for an edit would allow questions and answers to be improved without unnecessary modification and clutter, in addition to allowing smaller typos to be fixed.