Bannan is an 11 year veteran that specializes in stopping the run. The Chargers depth on the defensive line is paper-thin. They have a few undrafted free agents on the roster that are competing to get major playing time.
I like the undrafted guys, but having a guy with experience to compete for those positions will only strengthen the roster. If the undrafted guy wins the job over the vet, then all things are good.
Other than Jarius Wynn, the Chargers second team on the defensive line is full of undrafted rookies and practice squad players.