The amount of waste produced in the manufacture of a chemical product or a product of any kind should be minimized.  While one would intuit that this measure was always part of manufacturing efficiency, it was not. The introduction of the calculation of the E-Factor took the original form of:

E-Factor = kg waste / kg product

and can be adjusted to include a variety of aspects of the manufacturing process.  E-factor provides information that was historically neglected but is critical to moving toward more efficient and effective chemical production.