At this year's trade deadline, the Boston Celtics executed a series of transactions that allowed them to get under the luxury tax. They haven't just saved $325 million since last season ended. The franchise has now gained the ability to receive more salary than they send out in a trade. The organization also shed certain spending restrictions, and can sign anyone on the buyout market. Regarding the latter, keep in mind that they are carrying out a precise formula to remain under the tax.
Finishing this league year below that threshold would also put them in a position to reset the repeater tax.