Attic ventilation serves two purposes: removal of humidity and equalization of temperature.
If you don't have adequate ventilation, your attic will be warmer than freezing and will cause melting of snow on the roof. When the meltwater reaches the overhanging eaves, it either refreezes causing an ice dam, or drips causing icicles. In order to prevent this, the attic must remain below freezing, or nearly so.
(Well, technically, it's the roof surface that must remain below freezing. The attic can be somewhat warmer. But if the attic is too warm, that will prevent the roof surface from maintaining a subfreezing temperature.)
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.