@Senior2016M Yield offers somewhat valuable information because it shows which schools are the most desirable. There is a reason Harvard and Stanford have yields well over 80% while Yale and Princeton have yields <= 70%. Just to use your example, most people who get into both Harvard and Yale choose to go to Harvard, and also people are much more likely to turn down Yale for another ivy/top school than they are to turn down Harvard for another school.
Yield can be used as a proxy for the perceived strength of the school and the attractiveness of its brand.