Good timing Nick. I'm actually working on similar topics so I thought I would chime in with an excerpt here:
The regular applications of hormetic cold stress enhances our ability to preserve and generate heat when it's called for. For example, it prompts the contraction of muscles underneath hair follicles, closing the pores and generating heat in a more efficient manner via the burning of the then-acquired brown adipose tissues (a.k.a brown fat). In addition, cold stress triggers vasoconstriction (i.e., the constriction of blood vessels), minimizing heat loss during blood circulation, subsequently redirecting the heat to only the vital organs, making the body more efficient in heat conservation. In general, hypothermic conditioning has important implications in immune activation, weight loss and longevity.
As for vasoconstriction, Todd has already spelled out the precaution there. It is also worth notice that in a study, people who suffered angina actually do better in terms of surviving from future heart attacks, which, again, reminds us of the old saying that "what doesn't kill us makes us stronger".
You can also find out much more here