This process is known as reverse engineering or modeling and when utilized, new designs are improved and incorporated for engineering optimization of manufactured part. In production, the scanning is used to capture tooling or parts changes which occur in the production phase. Usually hand tuning is needed in tooling to get the desired finish and look of a given part.
When 3D comes into the picture, the optimizations and hand modifications are easy to transfer from tool to tool so all parts manufactured match after the production ends. The scans also help in analyzing and characterizing tool wear during the production; this is very helpful in correcting tool failure or eliminating the same before it is too late. It is actually very possible to recreate optimized part using a 3D scan.