The offense is mostly set, except for 3 or perhaps 4 back-up roster spots. There is a similar dynamic on the other side of the ball, too. The action here will be for scarce back-up positions and to establish rotational pecking orders.
The Chargers had to put a lot of spare parts, rookies, and FA's claimed off the scrap heap onto the field last year to play defense with the team's drafted veteran talent. This year, the front office and coaches hope that the growing pains of last season will pay dividends in performance this season.