Jon Brockman was perfect for the Sacramento Kings in 2009-10. With Spencer Hawes (one of the worst rebounding 7-footers in the league) as the presumptive starting center and only Jason Thompson, Sean May and a cavalcade of long small forwards at the power forward position, Brockman served as the antidote to the team's rebounding woes. As one of the league's best offensive rebounders from Day 1, as well as a decent defensive rebounder, in Brockman the Kings had a glass specialist, someone they could plug in when the shots weren't falling in order to get a few extra chances. It helped win some games, and helped build Brockman reputation and personal brand. (The bad-ass nickname suggested by Aykis and run with by the Kings didn't hurt, either.)
The Kings don't need a rebounding specialist any longer. Brockman may still have been a better offensive rebounder than any current King -- he really might be the best in the NBA -- but what Brockman offered is no longer a "need" in Sacramento. DeMarcus Cousins can rebound the hell out of the ball on both ends. Samuel Dalembert is one of the three best rebounders in the NBA, on both sides of the court. Hawes is gone, and the Donte Greene/Omri Casspi experiments at power forward are likely over, so the only time the frontcourt will be lacking in rebounding at one of the two positions is in Carl Landry's minutes. If Dalembert or Cousins is at center (likely -- these are the team's two centers now, no matter whether Thompson is better suited there or not), the rebounding won't be an issue.
A rebounding specialist isn't needed here. But a few other types of specialists do make sense.
A perimeter defender. The Ime Udoka/Desmond Mason special. (Heck, toss in Dominic McGuire.) A player who can come in and shut down a hot opponent. The Kings don't have such a player; Francisco Garcia may be an alright defender, or perhaps even "good." But he'll be asked to handle much of the offensive duties while on the court. Greene may be the closest player Sacramento has to the perimeter defender specialist trope.
A shooter. Kyle Korver, Jason Kapono, Eddie House. A player who can come in and let it fly. Typically a shooting specialist because they suck on defense and have trouble driving the lane or passing.
Change-of-pace point guard. This was Sergio Rodriguez. The unfortunate thing is that Sergio actually played well in Sacramento last year; with Beno Udrih and Tyreke Evans, and the team apparently wanting to put a traditional shooting guard in the starting five with Evans eventually, there just wasn't a reason to hang on to Spanish Chocolate. With Evans, a bully, and Beno, a pick-and-roll gunner, soaking up minutes, there's room for a lightning quick point guard behind them. The problem? Few are available.
The Kings may not find any of those specialists on the market right now. But -- depending on what happens with Landry and Dalembert next summer -- it looks like those will be the needs going forward as the Kings transition from rebuilding team to potential playoff team. Brockman just didn't fit a need, and his "upside" wasn't so great you could justify keeping him around "just in case." The Kings would have been short-sighted to keep him in this environment.