Each NFL offseason, fans enter free agency focused on what their teams can do to get better. But if there's one thing that can't be overstated when it comes to building a roster, it's the importance of retaining your own good players.

Ideally you re-sign them, but in a sport where careers are short, hometown discounts are largely avoided as players make the most of their peak earning years. It means teams need to use what leverage they have, and that is where the franchise tag comes in. The tag is a useful tool for holding onto a player for one more year and buying yourself some more time to negotiate or giving you the option of getting something out of him.

Let's take a look around the league at five players on whom teams should use the franchise tag, and five whom teams shouldn't.

Note: Salary cap numbers taken from www.overthecap.com

Tag them or else

Baltimore Ravens: Eugene Monroe

Cap situation: The Ravens have $12 million in cap space and 20 roster spots to fill. Savings would likely come in the form of cutting Jameel McClain ($3M) and Vonta Leach ($1.7M).

Analysis: They don't have a lot of room for maneuvering here, so the idea would be signing a deal and then using that as a springboard for a longer-term deal, though that would hand the leverage to Monroe and his agents. Simply put, the Ravens can't let him get away because he means far too much to Joe Flacco. Monroe's time with the team last season earned him the seventh-highest pass-blocking grade of all left tackles, and Flacco saw his QB rating drop to a woeful 46.7 when pressured. It's not just about the player, but what he means to the team.

Buffalo Bills: