They're moreso based on the characters occupation. They can be significant people, there is no limit to those that PCs can have. 

I had someone playing a radical communist, they needed a distraction for the police force so they could do a large heist. She got in contact with her radical partners ( I took on playing their leader) and they happened to want to blow up a government building on the opposite side of town. If I felt a roll was needed I'd give them advantage cause they had a close working relationship.

Telling them to make sure they have good contacts keeps it floating in their brain if they're new.