Evra's contract has no bearing on Shaw's signing because we need cover at left back regardless and having an experienced player like Evra who can start for a run of games if Shaw dips in form or has an injury is a fantastic option to have. Evra playing 30+ games is not an asset any more, but Evra playing 15-20 games is a massive boost to the overall strength of the backline. Evra also is somebody that seems to be a real positive to the morale of the squad overall which is something that is hard to quantify but is evident in his attitude and comments about the club. It's also likely this makes Buttner expendable, which is fine since I'd rather have Evra as cover over him. Evra is also a physical freak and if he is okay with playing a reduced number of games he can play another 3-4 years.