Earlier in the season, Boston offered Kenny Perkins a contract extension, which he declined. Perkins said no because the extension that the Celtics offered, whilst the maximum they were allowed to offer under CBA extension rules, was probably lower than what Perkins could corral in the summertime on the open market. But by creating this small amount of cap room, OKC can now offer him a bigger extension than Boston could.
NBA contracts are only renegotiable if
a) they're going upwards, and
b) the team has cap room.
Because teams so rarely have cap room, and because it rarely behooves teams to pay their already-under-contract players more money, it almost never happens. Indeed, before this season, I could not name you a single occurrence of it happening; it probably has at some point, yet that's a testament to how rare it is. However, in this modern, sabermetric, MIT-laden internet-era NBA, executives are far more cap creative than they used to be. Therefore, this barely-used strategy has been used twice far already this season. Washington used their leftover cap room to increase Andray Blatche's salary, almost doubling his pay over the final two seasons of his contract and simultaneously tacking on a three year extension. Rather than chancing losing him on the 2012 open market, the team tied him in for five years for a total of $35,730,997, tying down a productive young player for a significant period of time. The Thunder themselves later one-upped this move with a $17.55 million extension for Collison that deliberately, humorously and yet craftily made him the fourth highest paid centre in the world ($13,670,000), behind only Amare Stoudemire ($16,486,611), Dwight Howard ($16,647,180) and Yao Ming ($17,686,100).
By simultaneously acquiring cap space with the underpaid Kenny Perk, OKC can now do a Baltche with him. OKC can use their cap space to renegotiate Perkins's current $4,640,208 salary up to as much $6,696,720. From there, they can concurrently offer a new four year extension totalling a a maximum of $33,818,436, or any number below that that they feel happier with.
Add in the extra negotiated salary, and that's over $35 million for four years that OKC can theoretically offer him, as-near-as-is $9 million per. In contrast, Boston could only offer circa $6 million per. It's a significant difference.
If Perkins thinks he can get that much on the open market, he's wrong. He's not even worth that much, especially with his current injury concerns. Yet if OKC anticipates his return to full health, and wants to tie in the defensive centrepiece that they have thus far lacked during the entire Kevin Durant era without running the risk of him hitting the open market, they can do so right now.