If you don't have quality bodies on your defensive line, your defense will not succeed. It's that simple. For the Dallas Cowboys, it was essential that this particular group was addressed, especially on the interior. Dallas made a big addition, literally, when they traded for Jordan Phillips, who is 6'6" and 340 pounds with flexibility to play all across the defensive line. However, the Cowboys still needed an anchor at the one-tech who could clog up lanes and take on double teams. That's where Linval Joseph comes into play.
The Cowboys added the 6'4", 330-pounder to the mix as well.