As jtk says, it's about clients.
When I was hustling, mid 70s, it seemed to me that wedding photographers only saw the bride and groom, plus maybe immediate family, as clients. For me, everybody at the wedding was a potential client, including the kids. 'You look so sweet in that dress, ask your mother if I can take some pictures of you'.
I worked on spec. Informal/candid shots outside the church. At the evening reception I'd collect as many names and addresses as I could by doing b+w walkie snaps. 'My numbers on your receipt. Give me a call in a week or two if want to see the wedding photos I took earlier today.'
There was some legwork involved in flogging the colour prints but hey, work is work. In just about every wedding I wangled myself an invite to, more people saw the pics I took than those taken by the pro.