Substitutions at the college level can be very situational. If you have balanced midfield lines, using full lines can help keep players fresh and wear down an opponent.
If you have a center draw specialist or even two of them, you can run two mini lines.
Balanced midfield lines can be especially useful when your team likes to ride because the midfielders are constantly working hard.
Running lines also gives more players experience and forces them to be ready when their number is called.