When the rules stop being enough
Rule-based automation works until the exceptions outnumber the rules. Then you have a system nobody dares change and a person handling everything it kicks out.
The tasks worth automating with AI are the ones that were never quite rule-shaped: reading a supplier invoice that arrives in a different format each time, deciding which team a ticket belongs to, matching payments to orders when the reference is wrong. We start with a measured baseline of how long it takes today.