There are a number of reasons for considering subgroup results. For example, the criterion might be different for each subgroup, such as when the college first-year GPAs for engineering majors differ from the first-year GPAs of education majors.
It is also appropriate to consider subgroup results when it is suspected that one or more of the predictors might function differently for each subgroup. This could be the case with high school GPA, which may give a different result for older applicants, who have been out of high school for a few years, than for younger applicants recently graduating from high school.
Although you will probably not use separate prediction equations for admission purposes, information provided about subgroup performance may be of interest to you in monitoring how special groups of students, perhaps ethnic or gender groups, perform after they are admitted into your institution. If the particular subgroup's actual performance is considerably above or below its predicted performance, you may want to pursue possible explanations for this outcome.