Swedes loves to plan. Summer holidays are booked in January, dinner reservations booked 4 weeks in advance and all this is executed and discussed in the context of week numbers.
Sure you may have them too in your email calendar, but you don’t let it contextualise your life. Unless, you happened to be in Sweden. No one knows the date of their holiday plans but they will for sure know the week number when they are traveling.
"Want to grab a coffee? How about Friday week 17!”