Beyond arbitration, all of this makes the timing of signing of draftees extremely important. This is much more Cam Hope’s area of expertise than it is mine, but I will try to explain by using an example. A team that signs a top pick in the year that he is 19 is in a much better position long run than if they sign him at age 20. For example, let’s say that Dylan McIlrath is destined to be a star in the NHL (I am not saying that he is or isn’t, but its a very useful example). McIlrath is born on April 20, 1992. If the Rangers waited to sign him until next Spring just before they had to or at any time after December 31, 2011, he will be age 20 at the time of the signing for the purposes of arbitration. Therefore, all the years of his professional play would count towards arbitration, even if that play it is not in the NHL. With a player like McIlrath, who the Rangers believe has a good chance of becoming a top NHLer but may take awhile to develop, it behooved them to sign him before the end of this calendar year. And so they signed him in March 2011. It is not important to do this with players who are not expected to be top players, as the team wants to watch and see if they develop as expected, but for players who could wind up being elite, especially if they are expected to spend some time in the AHL, signing the player before he is 20 is an imperative.
You get seven years of "guaranteed" service. From 18 to 25, from 19 to 26 or from 20 to 27. Nothing complicated.
The 20 to 27 may be a bit better as the player is more mature, closer to his peak.
Signing him now changed nothing, it changes once he accrues the season (40 games on the roster)
The advantage to signing him now is that they would have the ability to slide his contract for two years if necessary. If they waited until after he turned 19 this winter they would only have the ability to slide the contract this year. I don't think that would be an issue for them, but that would be the advantage.