Low season also has its advantages. You have more space for yourself. Parks and museums are well below its maximum capacity. What will be queues and noise in summer, it is quietude and fast access in winter.
I have been in August in Japan. That month is hot and humid making it a lousy time for walking around. And there are the insects. I have mixed feelings about them. I like to hear the cicadas. But it is not a nice feeling when one of them lands over your clothes.
For me, it is not a real choice, anyway. Stockholm is dark in December. In the city, around 14:00 is already night time. And even when there is a sunny day, you cannot feel that warming sensation that should go with the sun. So, for all of its drawbacks, December is my preferred season to leave Sweden and travel.