The deal
Nuggets get: Center Roy Hibbert
Bucks get: Protected second-round pick
Denver Nuggets: A
The primary motivation for the Nuggets to make this trade was financial. Denver began the day about $7 million short of the NBA's minimum team salary, or salary floor, as it's colloquially known. Any amount short of that is paid by the team and distributed among its players.
Because the minimum is determined by salary on the books rather than salary paid, the Nuggets get to count Hibbert's full $5 million salary while paying him $1.4 million the remainder of the season (via Albert Nahmad) and saving the other $3.6 million.
Apparently Denver may have some interest in Hibbert as insurance at center, however. According to ESPN's Chris Haynes, the Nuggets could also have dealt for injured Portland Trail Blazers center Festus Ezeli and saved even more money (about $5 million, by my calculations) but chose Hibbert because he's healthy.
Milwaukee Bucks: B
After dealing for Hibbert and Spencer Hawes from the Charlotte Hornets in the recent Miles Plumlee trade, the Bucks had a whopping five centers among their 15 roster spots. Given the crowd, Hibbert was never likely to see the court in Milwaukee, and the Bucks save his salary the remainder of the season while clearing a roster spot to better balance things out.
The heavily protected 2019 second-round pick had to be involved to make this trade legal and will almost certainly never change hands.