All connections through Frankfurt (and probably other German airports as well) is subject to a transfer tax. This tax was the equivalent of SEK 85 for each stop last time I flew through there. So if you are connecting through Frankfurt both ways, thats another SEK 170 in taxes for your pleasure of being transferred by a bus instead of getting straight to the gate, walking their long walkways, being searched by their nazi-style security and peeing in their loos. Personally I don't think its worth it. Other airports (such as CPH) don't charge for transit passangers.