When looking at which offseason NBA deals have the potential to be the most impactful, you have to step back and define what "impact" means for each particular team's situation. The state of the league is such that the 30 franchises have distinctly different agendas, ranging from gunning for a title to tearing everything down to start anew. Measuring the impact of deals requires an understanding of the franchise's goal and how realistic the team's chances are of achieving it.
The method by which teams attempt to upgrade their rosters also plays a major role in defining their success or failure. There are three avenues NBA teams can embark on to import talent to their rosters: the draft, free agency or via trade. Each brings distinct pros and cons, and each can affect team success in its own way.
The draft is cheapest way to bring in talent, offers a chance to mold a young player into the vision of a franchise's culture and is the best way of keeping talent in-house for the longest period of time (rookie scale plus rookie extension) while still maintaining enormous contractual flexibility for the first four years of the deal.
Using free agency, a team can acquire a player whose track record is known, and a free agent is the most likely to make an immediate impact. But free agency is incredibly expensive, mistakes are harder to recover from, and a team needs to have the financial wherewithal (i.e. ability to pay, cap space to afford, etc.) to complete the transaction.
Trading for a player also provides a way to acquire a guy whose track record is known. Theoretically, a team can target exactly the player it wants and, based on his past performance, can more quickly nail down the right role for a player, facilitating his impact. However, you obviously need another team to complete a deal, and trades often involve some measure of roster upheaval, so chemistry issues can slow down or even impede the desired progress.
Now that we've clarified that "impact" is different for each club and outlined the methods by which a roster can be changed, let's look at the 10 most impactful roster moves of summer 2013. (For the purposes of this exercise, we are considering only individual transactions -- but keep in mind the transaction might net multiple players.)
The Rockets made the proverbial slam dunk move by signing Howard, an elite prospect in the prime years of his career. Howard provides the perfect interior counterbalance to last season's perimeter-oriented attack, led by All-Star guard James Harden. Moreover, he provides a much-needed defensive anchor and rebounding presence, far beyond what Omer Asik can offer. The cost for acquiring Howard was a maximum allowable contract plus the relinquishing of smaller assets (like Thomas Robinson) to clear cap space. The financial commitment is hefty, but it's worth it when you know you are bringing in bona fide talent that will make you better today and in the long run.