However, this may not result in the desired improvement in admission chances, if the additional schools are less correlated because they emphasize applicant aspects that the applicant is weaker in, with less emphasis on aspects that the applicant is stronger in (presuming that the applicant already has on the list those schools which favor the applicant’s strengths).
For example, if a California resident who is GPA-heavy (relative to test scores) has several UCs on his/her application list, adding USC may not improve chances much, since USC tends to favor test scores. But a test-score-heavy applicant may benefit from adding USC to a list that otherwise is made up of UCs, which tend to favor GPA.