I know that if
all things being equal (fabrics, thickness, and insulation), mittens are warmer than gloves.
from this question.
However, I feel like there's was a trend to "mittens" the last years. It's unlikely that this only comes from the fact that "mittens are warmer" cause it's not that of a problem (in common) while snowboarding.
In which circumstances are they preferable over common gloves?
Or is it just a matter of personal style preference?
I ask from a snowboarding point of view: