Enthusiasm
1. TIE increases it by 1/3 after the game.
2. CT decreases it by 1/2 after the game.
No matter what enthu you have, it will slowly gravitate everyday towards 5. The general belief is that enthusiasm helps increase player's performance in rebounding, and inside/outside defense as can be observed through game ratings (I have my own set of beliefs though). Games between evenly matched teams can easily be decided through enthusiasm differences, especially big ones.
It is also believed that TIE-ing a game while you have 8 enthusiasm can make your players play the same way as you Normal-ing with 5 enthu. But choose TIE, Normal, CT wisely. Losing games at the top level, the MBBA for example, at the expense of TIE-ing, can mean the difference between relegating and staying up (relegating hits a well established MBBA team hard financially). Losing to a rival, or an away game also affects income (merchandise and next home game receipt).