Most toilet clogs are isolated. Something got stuck, a plunger clears it, and that's the end of it. But if a toilet backup shows up alongside slow drains in the sink or tub, or if more than one fixture is acting up at the same time, that's usually a sign the problem isn't the toilet itself but the main line it feeds into.
When several fixtures back up together, water and waste have nowhere to go because something further down the system is blocked. That's a case where a camera inspection makes more sense than repeated plunging, since it shows exactly where the real blockage is instead of just treating the symptom.
