Although I am not a graphic designer, I often end up referring to design branding materials for various reasons. In my experience, many brand guideline documents have a Fonts section, which specifies which fonts should be used to remain on-brand. This list usually includes two or three fonts, and the font which is used for the logo. However, there is usually a comment alongside the logo font saying that it should be used only for the logo, and not for other branding items.
I believe that this is fairly common - I can't think of any brands that do use their logo fonts elsewhere. It seems fairly sensible, but arguably, the logo typeface could be used elsewhere to "continue" the brand. I'd like to know: what is the formal reasoning behind this decision?