SAS calls it's seating Go, GO plus and Business versus the more conventional Coach, Business and First. [Business on SAS is a wrap around reclining sleeper.] Prevalent coach is adequate but crowded, noisy and includes no frills. Buy your meal, entertainment and even soft drinks. OK for short trips, but likely to result in a miserable arrival on long flight. My seat was initially booked in the middle of the coach section of a long transatlantic flight. a situation I dreaded.
As it happened, I was standing beside the counter, when the attendant said they had upgrades available for a fee. Considering that a Plus seat would have doubled my initial airfare coast but a counter upgrade was less than half, I took the offer. The upgrading includes not only a larger seat in a less crowded area but also use of the pre-flight lounge and on the plane all food, drink and internet, items for which you otherwise would have to pay.
While we all want to save on our airfare, consider the quality of your travel as well. For long haul flights an discounted upgrade may well be worth it.