Every NBA team trades draft picks at some point. They are extremely useful in the market: enough first-round picks can land you a big name player if you have an expiring contract, movable matching contracts or cap space to take him on. (The Celtics traded Kevin Garnett and Paul Pierce largely for multiple first-rounders.) A second-round pick or two can get you a starter, in many cases. (The Blazers traded a future second-rounder and Jeff Withey -- who just went No. 39 in June -- for Robin Lopez. The Kings picked up Luc Richard Mbah a Moute for two second-rounders.) Picks can be protected to ensure you don't give up what eventually becomes Kyrie Irving (whoops!). Or, they can be unprotected, which carries more value.
But increasingly, teams are also using the pick swap option in deals. (It's not a new phenomenon by any stroke of the imagination. But it's really common now.) It provides the receiving team the ability to switch first-round picks with the other team. For instance, the KG-Pierce deal includes a pick swap option for the Celtics in 2017. If the Nets' pick is to be higher than that of the Celtics, Boston will use Brooklyn's pick and give the Nets their own.
In that way, the team that conceded the pick swap option ensures it keeps a first-round pick; it just may be lower than it otherwise would have been. It also helps to get around the Stepien Rule, which bars teams for trading future first-round picks from consecutive years. The Nets traded their 2014, 2016 and 2018 first-round selections to Boston. The Stepien Rule prevents them from trading their 2015, 2017 and 2019 picks to the Celtics (or anyone). But the Stepien Rule doesn't block the pick swap option, because the Nets will still have a pick that year.
The question is whether the team giving up the option is really losing much, and whether the team taking it is gaining much.
When you trade for a draft pick, you know you're getting an asset. There may be some calculus in choosing a year in which it is more likely your trading partner will be poorer (and thus, give up a better pick), but regardless, you're getting an asset, whether it's top five or No. 29. But the pick swap option takes it a step further. It's a game within the game because you're betting on two things: that the trading partner won't be great and that you'll be decent. The swap option only means anything if you're better than the partner.
That's why the pick swap option really has to be treated like a sweetener more than anything. The option itself can't go wrong: if the team guesses wrong and ends up with a better pick than the partner, oh well. The teams keep their picks. But if the overall value of the trade depends on getting value out of the swap, you're playing with fire.
Keep in mind that your pick being better than that of the trading partner means that in the time since the trade, the partner has been better than you. If it's been a long time -- like the four years in the Boston-Brooklyn example -- that doesn't speak well to the results of the trade or your own work to rebuild your team.