The Lions have a lot of young players to make calls on in the very near future. Some of them, like Louis Delmas, are unrestricted free agents, and therefore very difficult decisions.
Some, like Joique Bell, are exclusive-rights free agents, which makes the call a little easier. Bell's play, however flawed, was more than sufficient to justify bringing him back for another season (or more), as he was arguably the Lions' most effective backfield threat this season.
Ricardo Silva is another ERFA who the Lions are likely to bring back on the cheap.
But then there are players like Amari Spievey, who is a restricted free agent, but whose play makes him a big long-term question mark. Do the Lions want to invest another year in seeing if he can get it figured out?
What about Jason Fox? Willie Young? Lots of potential, but are they worth the money and the roster spot?
Ultimately, the answer is almost always yes, especially since these players all play at positions with a lot of potential turnover and uncertainty. Unless they're really good, most young free agents with some sort of restriction can be signed on for salaries ranging in the hundred-thousands.
That's not going to break the Lions' salary cap, and each of these players have the ability to play large roles for the 2013 Lions (and beyond). As long as the investment isn't too high to find out, why wouldn't they give these guys another shot?
Even if each of these players tanks in 2013, the Lions aren't losing a major investment (unless it's a high draft pick like Spievey, but that's a different kind of investment). They're basically betting on these guys with house money at this point, so until they give the team a reason to cut them, the Lions have no reason not to let them ride.