Certain job specific frequencies often go unused

[DimWhat]

You also need to take into consideration how the departements work, in Research and Medical for example, constant radio chatter isn't always necassery, often times your colleague is around the corner unlike for example Security where each officer might be patrolling on seperate parts of the station.

Wow this is a really good way to see it. Medical is generally able to easily communicate what's wrong to eachother due to how much of the equipment is in the medbay. And most of of sci's stuff is hanging around in one spot.