In the real world, it's usually better to get your holiday shopping done as early as possible. In the NFL, the opposite might be true. You don't want to wait until the last possible second to sign somebody to your roster, but smart organizations often take it easy during the opening days of free agency before pouncing later in the offseason.
For those teams, it's not just about whom you sign. When you sign a player matters, too. Organizations like the Rams and Ravens focus on the compensatory pick formula, which allows them to get draft picks in return for the players they lose in free agency.