+1 I don't gain anything by taking the SK flight vs. any other airline. I have done LX, LH, AF, TK, SK+UA, DL. The earliest is LH - departing at 6am, which is damn hard, especially when you are travelling with kids and they don't sleep during the flight.
I do like the late departure ex-LAX (such as TK and LX, or LH via MUC) because as Tango Alpha said that you could use that day in LA before heading to LAX. Flying at 14:00 means you get up and it's almost time to go to the airport = a whole day wasted.
Maybe the flight is design for people who need to fly into ARN to have meetings at the airport. Mr. Nacho has done that several times - all the Nordic departments meet at ARN instead of the HQ in DT Stockholm.