On the surface - not much. One is an athletic big man who earns his money rebounding and fitting into the Cavs' defensive schemes. The other is a wing collecting a paycheck with his outside shooting and quick hands on the perimeter.
But take a look at the contract and a commonality emerges: Thompson and Crabbe are both being paid big money through 2020 to be role players/fringe starters for their respective teams.
In the case of Thompson, Cleveland's decision to offer their center a 5-year, $82 million contract last summer was widely questioned. As several media outlets pointed out, including Blazer's Edge, his production prior to the new contract was nearly identical to Ed Davis. In comparison, Davis signed a 3-year, $20 million contract last summer. Yikes.
So this is a clear cut case of the Cavs stupidly overpaying a role player, right? Not quite. Many Cavs fans have argued that the signing was actually a smart move - even the obvious choice. That logic revolves around the fact that the Cavs were already over the salary cap before they re-signed Thompson. Teams in their situation are restricted to using minimum contracts and low-dollar cap exceptions to add new players, so the Cavs had to take advantage of their ability to exceed the cap to re-sign their own free agent or lose a key role player from their team, even if it meant significant over-payment. Thompson's agent, understanding this reality, held out for the most money he could possibly earn for his client. The result: $82 million for a $40 million player.
The Cavs' conundrum revealed a quirk of the NBA's salary cap rules: Once a team is one dollar over the salary cap they should overpay to retain their own semi-valuable free agent as there will be no other way to replace that player. (Note that this assumes the owner is willing to pay the extra salary and that the team is not exceeding the luxury tax threshold.) Further, if a team does not retain their free agents, they have reduced trade flexibility as they cannot take on additional salary in a trade and have fewer players to trade. In short, being one dollar over the salary cap and letting a free agent walk arguably puts a team in a worse short-term situation than retaining the player and being near the luxury tax.
So how does all of this apply to Crabbe and the Blazers? Without Crabbe's contract the Blazers would only have about $4 million or $8 million in cap space, depending on whether or not Moe Harkless signs his qualifying offer. Finding a player of Crabbe's caliber with a $4 million or $8 million pricetag would have been nearly impossible. Crabbe also provides skills the Blazers desperately need. Swapping out Gerald Henderson for Evan Turner certainly improved Portland's ballhandling but did nothing for their outside shooting. Crabbe is the only reliable 3-point shooting wing on the roster, and as such his floor spacing abilities are immensely valuable. Crabbe's additional salary also gives President of Basketball Operations Neil Olshey another trade chip should a blockbuster deal present itself in the near future.
Olshey likely did this mental calculus and decided that overpaying Crabbe and exceeding the cap was a better option than hanging on to a few million in cap space that could only really be used to acquire bargain basement veterans, or long-term project players.
That said, the circumstances surrounding the decision to re-sign Crabbe and Thompson are not entirely identical for the Blazers and Cavs. In 2015, Cleveland had championship aspirations after losing the Finals sans two all-stars. Most believed that they were one or two players and some better injury luck away from winning a title. Under those circumstances, there's a lot more pressure to go "all-in" retaining useful players. The Blazers are obviously not challenging for a championship right now, but can still justify this decision by pointing out that the free agent shelves had been more or less picked clean so overpaying for Crabbe was essential to helping the team win next year.
It's important to acknowledge that extending Crabbe was not a no-sacrifice decision for the Blazers. When the Cavs re-signed Thompson they were already guaranteed to be in excess of the cap this summer by virtue of their existing contracts. His deal did nothing to their long-term flexibility.
Crabbe's contract, on the other hand, has some salary cap implications for the Blazers next summer. Without Crabbe on the books, and after making obvious personnel decisions such as extending qualifying offers to Mason Plumlee and CJ McCollum and picking up Noah Vonleh's team option, the Blazers would have about $92 million in cap space locked up. That would have given them about $10 million in cap space at the league's current estimate of $102 million, or $18 million if they elect not to bring back Festus Ezeli. It's possible, if not likely, that the salary cap numbers will spike again after the league and players re-negotiate the collective bargaining agreement, which would have given the Blazers even more cap space. This suggests that Olshey decided the value he could get for Crabbe immediately outweighed having an undetermined amount of cap flexibility next summer. Given the Blazers' free agent history, Turner notwithstanding, and the uncertainty involved in waiting for more cap space, that decision is defensible.
More concerning is the Blazers' luxury tax future. Assuming the league's $102 million cap estimate for next summer is accurate, the luxury tax will be set at about $122 million. The Blazers already have about $89 million in guaranteed contracts next summer. Throw in McCollum's presumable $25 million extension and that figure rises to $114 million, BEFORE accounting for Ezeli's non-guaranteed salary, Vonleh's team option, Plumlee's qualifying offer, or any money owed to a first round draft pick. Add in those obligations and the Blazers' salary swells to at least $130 million - at least $8 million over the low-end luxury tax threshold. Crabbe's deal all but guarantees the Blazers will be at or near the luxury tax next year, unless they make more major changes to the roster or the league's cap rules are drastically altered.
So, was matching Crabbe's contract worth it from a salary cap perspective for the Blazers? Tristan Thompson and the Cavaliers provide some precedent to explain that the answer is a resounding "YES" over the next 365 days. But that decision may become less palatable next summer as the Blazers, unlike the Cavs, are not in the position to win a title immediately, and must still make choices about whether or not to pass the luxury tax threshold to retain Ezeli, McCollum, Vonleh, Plumlee and others.