The source was the swedish military webside, and it was officers on the swedish sub that said it. They also said that they sinked the carrier 5 times, and all times got away with it, and most times got away unspotted!
Off course you can not lurk around in real world on battery only, and then get a carrier group lined up in front off you ready to be blown up. But if you are so lucky, then the carrier group have a very big problem.

The best thing with an SSK is the potential treat of if its nearby. A carriergroup reach coast of Norway, and knows 3 subs are out on patrols, they have no idea where those 3 subs are, and have to plan theire operations accordingly.
They have to be farther away from land, conduct much more sub patrolling etc.
In essence, they cant operate in a manner that is the most effective for operation over land.