One of the things that rookie RB tend to struggle with is pass protection. So having a veteran such as Murray who did well in that area last season give the Vikings a player they can count on to help protect Sam Bradford until they do feel comfortable with a rookie RB in pass protection.
The deal is structured so the Vikings can move on after this season without being on the hook for much in terms of cap space after this season. So if the Vikings do draft a RB who can beat out Murray and McKinnon, they can just let Murray go or keep him for depth. I see him as a bridge to a new RB to be drafted either in 2017 or 2018.
Murray does have a speed element that could lead to some long runs if they can make some holes for him. He isn't a very elusive player and a bit tall for the position which makes him a bigger target for defenders. He isn't going to create a lot of space for himself on his own. He is a complete RB in the sense that he can be used on all 3 downs. A decent receiveing and blocking option in the passing game, runs well out of the shotgun formation.
After the Vikings signings they have $18 million left in cap space for 2017 according to
this. There are some ways to save money, such as restructuring Brian Robisons contract. I think most of that money remaining needs to be reserved for new contracts with Xavier Rhodes and Sam Bradford.
It is possible they sign a linebacker for depth still but none on the free agent market really stand out.
Nick Mangold is available and could provide more veteran depth to the offensive line. Not sure if there is any mutual interest or what kind of money Mangold is looking for though.