If you turn it on, use one of the last two (added teams) being VAN or WSH, play a game, then check the win loss ratios of the teams you will see that VAN or WSH percentages etc. will be wrong.
This is because the game only ever made the battery backup expecting only 28 teams. The above is a simple example of potential corruption to the battery backup data. There may be more corruption when it goes to save player data for these teams? Over extended use, this could completely stuff your games save. It might work. It might not. I wasn't going to test it until the cows came home because the the team win/lose ratio stuff up was enough for me to work out it might not best to leave on the User Records.... that why you "Leave Off!"
and no, I don't think I'll ever work out how to make the battery allocation bigger to support 30 teams properly...