The deal
Cavaliers get: Rights to Dimitrios Agravanis and Sergii Gladyr
Hawks get: Guard Kay Felder, forward Richard Jefferson, worse of Lakers' or Timberwolves' 2019 second-round picks, the Trail Blazers' 2020 second-round pick (top-55 protected), cash
Atlanta Hawks: B-

According to a report by ESPN's Adrian Wojnarowski, Atlanta plans to waive both Felder and Jefferson before Monday's deadline to set rosters for the 2017-18 regular season, meaning this trade was entirely about the two second-round picks the Hawks acquired. (The cash covers the $3 million Atlanta will have to pay Felder, whose contract is partially guaranteed for less than $500,000, and Jefferson.)
The timing of this trade is key for the Hawks. Taking on the salaries of Felder and Jefferson just about exhausted their remaining cap space, and the upside of using that now rather than waiting into the season is Atlanta doesn't have to waive anyone to make room to add salary because the limit is still 20 players. (The Hawks had two roster spots open after letting John Jenkins and Jordan Mathews go last week.)
I actually would have preferred to keep Felder, who has shown some promise as a scorer off the bench, and waive European veteran Malcolm Delaney after an ineffective NBA rookie campaign that saw him rate 2.6 wins worse than replacement.
Still, this trade is primarily about the draft picks -- or more likely pick. The 2020 pick from the Blazers is one of the phony, top-55 protected picks that are exceedingly unlikely to ever transfer. The 2019 pick will probably come in the bottom 10-15 picks because it's the weaker of two originally belonging to the Lakers and Timberwolves.
Cleveland Cavaliers: A+

Trading Jefferson was always the most logical solution to Cleveland's roster crunch after adding Dwyane Wade gave the Cavaliers 16 guaranteed contracts. Cleveland couldn't trade newcomers Jose Calderon and Jeff Green until Dec. 15, leaving Jefferson as the tradable player least important to the team's long-term future. While the Cavaliers wouldn't have won a championship without Jefferson as a small-ball 4, that spot has been taken by Jae Crowder now, with Green as a cheaper alternative option. So perhaps the biggest loss here is Jefferson's ability to podcast with former teammate Channing Frye.
Felder's fate was already sealed, given his partial guarantee. As ESPN's Bobby Marks notes, trading both Felder and Jefferson instead of waiving them slices Cleveland's enormous tax bill -- still more than $40 million -- by nearly $13 million. That's well worth giving up what will probably be a late second-round pick.
Because the Cavaliers still have 15 guaranteed contracts and an enormous tax bill, it's unlikely the $2.6 million trade exception they generated by trading Jefferson (as well as a smaller, $1.4 million for Felder) will come into play this season.
Agravanis and Gladyr are the two international prospects whose rights the Hawks will send back to complete the trade. Gladyr is a part-time starter in France who has no NBA value. Agravanis, taken with the penultimate pick of the 2015 draft, is still just 22, so he's got an outside shot at developing into an NBA player down the line. But getting their rights was not part of Cleveland's reasoning for this trade.