regular season.

1- It would be considered by the selection committee as a good possibly great win. Likely Top 25 rpi win.
2- It would set up either another game against a quality opponent, or a cake walk to the finals (if somehow Chaminade pulls the major upset in round one.)
3- If BYU loses, they likely get a bad opponent in round 2, and an average opponent in round 3. They need to play and beat good teams. Losing to SDSU won't give them that chance.

Obviously ncaa tournament tickets aren't punched in November, but beating SDSU, and splitting the last 2 games would pay big time dividends come selection Sunday.