Clubs that have changed head coaches in the off-season are allowed a 14-day headstart by the NFL, and the Lions will look to rebuild under new coach Jim Caldwell after firing Jim Schwartz last season.
Mayhew told reporters: "It will give us an indication of some areas where maybe there's a young guy we really haven't counted on, who looks like he's going to take to a new system and going to be a really good player for us.
"Maybe there's a vet we are counting on we need to make some other plans for. There's always a benefit to having that early camp."
The Lions finished with a 7-9 record in the 2013 season.