Why it works for Allen. Scheduled to earn $585,000 this season, the third-year player almost certainly gets some up-front money he wouldn't have received otherwise. By cashing in now, he no longer assumes the risk of making it to restricted free agency next offseason or unrestricted free agency after the 2016 season, which is when he would have been in line for a new contract and has his greatest leverage, if still healthy and performing at a high level. But when a player cashes in early, he usually does so knowing that he could be leaving money on the table down the road.
Why it works for the Patriots. Allen has proved to be a solid punter for the club, and the Patriots would have had to consider tendering him at a second-round level next offseason ($2.356 million was the second-round tender level in 2015) as a restricted free agent to protect themselves from another team signing him away with an offer sheet. Because Allen entered the NFL as an undrafted free agent, had the Patriots tendered him at a level lower than the second round, they could have lost him to an offer sheet and received nothing in return, compensation-wise. By presumably paying some up-front money now, they take that scenario off the table.
Specialists locked up. With Allen in the fold for four more seasons and kicker Stephen Gostkowski and rookie snapper Joe Cardona also signed through 2018, the Patriots have their three specialists locked in.