Hypothetically, if OSU beats Illinois in this game and Purdue beats Wisconsin tonight and Indiana then OSU would be a #5 Seed in the Big Ten Tournament.
If OSU wins the Big Ten tournament defeating Northwestern/Minnesota, Purdue, Michigan, and Iowa along the way they would finish with an overall record of 23-7 (17-7 = 71% in Big Ten games). OSU would also improve to 10-5 in Quad 1 games.
If Illinois loses to OSU and then loses the first game in the BTT to Wisconsin/Indiana then Illinois would finish with an overall record of 19-8 (15-6 = 71% in Big Ten games). Illinois would finish 8-7 in Quad 1 games.
Looking at those 2 potential final resumes it seems pretty clear that OSU could finish ahead of Illinois if they win out and Illinois loses out... HOWEVER if Illinois wins this game the conversation dies.
If Illinois beats OSU and then loses the first game in the BTT to Wisconsin/Indiana then Illinois would finish with an overall record of 20-7 (16-5 = 76% in Big Ten games). Illinois would finish 9-6 in Quad 1 games.
Even if OSU wins the Big Ten tournament defeating Northwestern/Minnesota, Purdue, Michigan, and Iowa along the way they would finish with an overall record of 22-8 (16-8 = 67% in Big Ten games). OSU would also improve to 9-6 in Quad 1 games.
Illinois would have split the series with OSU and have the same Q1 record but have a stronger B10 slate which probably is enough to tip the scales in favor of the Illini.
TLDR: This game matters for killing OSU's hopes of taking the #1 seed from Illinois.