Not dumb question... maybe too much specific. Using of tracer ammunition is regulated by tactical manuals, to regret I have no anymore any of them. As I know it is used in belt or drum where is every fourth bullet tracer type. This is used in every condition, day or light and general purpose is to help to find quick path to target. As I know it is controlled by unit officer prior the missions.
Every armament could use it, does not depend of the position, fixed or flexible. Off course- lack of supply could mean no tracer...
Cheers