After arbitration I am over budget by 3k. I can move money over but curious if anything happens because of it

Not 100% sure, but I think:

1) won't be able to promote players (no room in budget for raise)
2) won't be able to sign additional players (no room in budget)
3) won't be able to sign draft picks (no room in budget for their salary)
4) won't be able to complete a trade that does not result getting within budget constraints (trades that result in out of budget are nullified)