Hopefully this question is answerable. When making up window trim, there is typically a small reveal between the jamb and the casing. Is there a reason for having this, other than aesthetics / tradition?
Possible things that came to my mind, but I don't know if these are valid: easier to install, easier to hide imperfections.
I found this image that should clarify which pieces I'm talking about - jamb and trim/casing.