Trying to filter noise from data also follows the 80,/20 principle. The rules for the easy cases is written easily but then you have one-offs, maybes and special cases. Trying to filter one of these does not cover anything else. So doing it manually takes the same time.

Case study: had to clean a list of German addresses once. Excluding obviously invalid addresses like some Chinese address was easy. But some addresses had errors which needed a human eye to fix and correct.