Fishing Line

I'll assume you're talking about on baitcasting tackle.
From our pros, I've surmised that:
Fluorocarbon is less visible, lower stretch, smaller diameter with more abrasion resistance than monofilament.
David Fritts has some interesting points about what he doesn't like about fluorocarbon, they are in one of these 2 videos:
https://bassu.tv/bass-fishing-video/cranking-secrets-david-fritts (I believe this one)
https://bassu.tv/bass-fishing-video/flat-side-crankbaits-with-david-fritts (possibly this one)