For the first time since the collective bargaining agreement was ratified in 2011, teams above the "tax apron" are blocked from acquiring players via sign and trade.
Last off-season, the Lakers brought in Steve Nash from the Phoenix Suns through sign and trade. Given the team's sizable payroll, a similar transaction might be impossible for the Lakers this summer.
The tax threshold is expected to come in at an estimated $71.5 million.  The apron will be set to $4 million over the threshold — or approximately $75.5 million.
The Lakers currently have $68.1 million in guaranteed salary for the coming year, more if Metta World Peace doesn't opt out of the final $7.7 million on his contract.
The Lakers hope to re-sign Dwight Howard for approximately $20.5 million.  With both Howard and World Peace under contract, the Lakers payroll would climb close to $100 million.
The Lakers still have their one-time amnesty, which could be used on Kobe Bryant, Steve Blake, Pau Gasol or World Peace.  If the team used it on one of the latter three, the Lakers' payroll would still sit over the apron.
It would take amnestying Bryant for the Lakers' payroll to shrink to about $70 million. While that might enable the team to make a sign and trade, it's not worth cutting ties with Bryant (despite his Achilles' injury).
If Howard returns, the Lakers are not going to be able to bring in a player via sign and trade.
Conversely, the Lakers are legally permitted to sign and trade Howard to another team. It's the acquiring of a player that is banned for teams above the tax apron.