Heavyweight odd waistcoats

[dsmolken]

I'm going to have a waistcoat made from overcoat material, more or less along the lines of Filson's western Mackinaw vest. It'll be charcoal. How, when and with what would you wear one? I have one fairly specific use for it, and can also use it for layering on cold days, but I'm wondering whether there are any rules or traditions, such as "heavy wool waistcoats are only for hunting".