Data may be wrong. Third, rankings are dangerous because the underlying data are not reliable. Different schools may have different ways of counting courses, faculty, students, or jobs. On top of those potential variations in approach, it is entirely possible for the administrator reporting the data to make a mistake that no-one catches. Real differences are small.
All rankings strip away information about differences in degree.
In some cases this makes law schools look more similar than they are, but in most cases it makes schools look more different in quality than they really are. Law schools vary more in character and style than they do in quality. Notice that many closely ranked schools have very similar total scores, and even schools with quite different rankings can have similar total scores. With an insignificant change in the data, such as two additional students passing the bar exam, a school could jump over competitors with similar total scores. In other words, rankings are dangerous because they mask the fact that the differences between schools are negligible on many criteria.