Cast iron corrodes from the inside out, and rust builds up along the pipe wall until the usable opening narrows well below what it was on the day it was installed. A camera inspection shows that narrowing directly instead of leaving it to guesswork.
Recurring clogs in the same section of line, a slow drain that no amount of cleaning fixes for long, or a rust-colored stain where the line runs are the usual signs that the pipe itself, not just what is inside it, has become the problem.
Not every cast iron line needs full replacement right away. A spot repair can address one bad section, but a camera inspection is what tells you whether that section is isolated or part of a longer pattern.
The camera footage becomes part of the conversation, not a verbal summary alone. Seeing the actual scale buildup or crack makes the choice between a spot repair and a full replacement a shared decision, not one taken on faith.