I agree when one is doing new development or can add the keys to an old system during conversion.
HOWEVER, when you have a Clipper system that has been in use for 17 years and converting the entire system will take 2-3 years, some proper design techniques have to wait. The problem is that some of the Clipper code has to run in parallel with the VFP code and without changing code in 2 systems, primary can only be used sparingly.
I'm posting this as an exception. After 15 years of working on lots of systems written by someone else, I've learned that "Never is a very long time!!!"