Currently standing at 20th in projected cap space (per Over The Cap), the rebuilding Panthers aren't exactly in need of a ton of room, but will send an in-his-prime guard west for a tackle who is six years older and in the last year of his contract. Okung has been solid for the Chargers, but this could be more about shedding a contract (Turner's) that carries a $12.8 million cap hit in 2020 and balloons to $15.39 million in 2021, creating cap space for 2021 and finding a stopgap at the position in the meantime.
The Chargers, meanwhile, are getting a rock-solid guard who could become a foundational piece as the team attempts to provide enough protection for whoever is lining up under center (currently it's Tyrod Taylor, but we're still free agency and the draft from that becoming certain). Los Angeles' selection of Forrest Lamp hasn't panned out due in part to injuries, and with a team that still has enough talent elsewhere to compete in 2020, adding a quality starter at guard is worth it -- especially after the team was forced to give starting reps to younger linemen as it dealt with Okung's injury struggles last season.
All deals aren't official until the start of the new league year, though, but right now this agreed-upon trade will shift notable linemen to opposite coasts.