Sweden was absolutely crucial in WWII, for one simple reason...
Nazi Germany was almost totally dependent on Sweden for it's supply of steel.
No steel - no armaments industry - game over, thanks for playing.
Sure, Sweden was technically neutral... but we know the Nazis did not respect neutrality. Holland was neutral. So were Denmark and Norway.
That didn't stop the Panzers rolling across their borders.
But Sweden was different. As long as the steel kept coming, the Nazis were happy enough to leave Sweden alone.
So, throughout WWII, Sweden was using steel to "buy peace".
The allies knew the importance of Sweden to German industry.
Churchill proposed a plan - called "R4" - to invade Sweden via Norway.
Fortunately, British military commanders advised that R4 was impossibly ambitious and that Britain's military resources were already overstretched.
But the Germans could not risk leaving Sweden undefended. They kept large numbers of troops in Denmark and Norway throughout the war, in the belief that Britain would try and cut off their steel supply.
British forces encouraged this belief with commando raids on the Norwegian coast and islands.
Entire German divisions in Scandinavia were effectively kept out of the war by a few commandos.
Hope that helps!
"The Second World War" by A.J.P. Taylor.