Big Swede, I would never go back to winter calving. The recent weather is a good reminder for that. Spring calving, 1st of April to mid May, has its fair share of issues but is still preferable to winter.
The pluses are... Longer days, shorter nights, usually warmer, when it gets cold it warms up in a few days or less, grass is starting to come along, usually get to quit feeding somewhere in the first cycle, winter husbandry on non lactating cows is easier and cheaper.
The reason I calve as early as April 1 is that here it is about the end of winter and I am trying to squeeze it in before putting the crop in. Otherwise it would be 3 weeks later. The calves are still capable of being fattened on grass with our resources by Sept the following year. June might take that enterprise away.
The negatives... could be scours. Our first case in several years of this management has yet to appear though. The key might be that they are moved from a smaller paddock to wide open spaces within a day of birth and the first and second calvers go to different paddocks than the older cows. There is always a Big wet snow event sometime during this period. I think it is a reminder of why we don't calve in the snow. My winter sheds and facilities can come in handy for these few days.
I'm sure there are a few more negatives but none come to mind right now. Overall it is just less work and takes less money.