A team often can fill its biggest needs in free agency, creating more flexibility when it comes time for the draft. In other words, the team can draft the best available player (in theory) without having to reach to address a need.
You can't say that about the New York Jets. They signed five free agents from other teams, including two wide receivers and a cornerback, but their top needs remain the same -- wide receiver, tight end and cornerback. This illustrates an absolute lack of depth at those positions.