Assigning players does not open up an NBA roster spot, as both are still technically under contract, so this isn’t necessarily a prelude to another move.
Brown, the 44th overall pick out of Oklahoma State, had yet to crack Lionel Hollins’s rotation, playing in just 38 minutes over 7 games, primarily in garbage time. Jefferson, the “Mr. Irrelevant” of the 2014 draft (he was picked last), had gotten a chance to play with the Nets injury-ridden, averaging 3.7 points and 2.3 rebounds in just under ten minutes per game over 15 games, making a name for himself for putting up arguably the worst shot in NBA history. Both will get more playing time in Maine, should the Nets elect to keep them there long-term.
The Maine Red Claws are technically not the Nets’ D-League affiliate: that’s the Fort Wayne Mad Ants. But the Nets share the Mad Ants affiliation with 11 other NBA teams, and the Mad Ants can only take on so many NBA players. The NBA allows those teams to do a “flexible” assignment, in the event that the Mad Ants have too many players assigned, and the Red Claws (operated by the Boston Celtics) took them on.