An example might be the designer of a structural component who went through a prototype program and initial prototypes failed in mechanical testing. A subsequent redesign yielded parts that performed well. The designer however, had prototyped the initial parts in an alloy and process that was not representative of the eventual production process.
Although on the surface this resulting redesign may not seem to be a big deal, it may have been totally unnecessary. Imagine also, that this over design caused by the non-representative prototypes added $4.00 to the production cost of each part. Certainly an issue if you are looking at an annual production rate of 500,000 parts.
Another is the designer that prototyped in a material whose heat dissipation characteristics were greater than that of the eventual production material. Imagine the anguish as parts “in the field” failed after prototypes had performed well. This is obviously another situation to avoid.