Well he was already Oiler property, he was a 2nd round pick a year ago. However getting him under contract is a good thing, very solid prospect. Here's part of his bio from Hockey's Future:
Musil boasts good size, is near NHL ready as a teenager, and is a strong character-guy. Primarily considered a shutdown defender at this point, he has good puck skills and an offensive side that could evolve over the next few years, however it is unlikely he will be a big time scorer at the NHL level. He plays a smart, contained, physical brand of hockey, boasts NHL bloodlines (son of Frank Musil), and has a skill set that should translate incredibly well at the pro level. He has had some issues with injuries in junior, which is never good, however has thus far avoided anything too serious.
We could see him patrolling an NHL blueliner sooner than much of his draft cohort. He doesn't need to add size as his frame is NHL ready, nor does he have any glaring weaknesses in his game to correct. Perhaps more importantly, Musil is a physical, stay at home, defensive defenseman, a role not found in abundance on the Oilers pro roster or in their prospect ranks. He will likely turn pro in the 2012-13 season and could be in the NHL as a regular as early as the following year.
He won't play with the main club for several years, if at all. However, signing a draft pick to a contract is always good because it shows the organization is sufficiently happy with his progress that they are willing to pay him money (I believe there are signing bonuses he receives even if he never plays for the team). It also means the player wants to play for the team, which is the case 99% of the time anyway. (A 1% example would be someone like Schultz, who for some reason does not want to play for Anaheim).