The biggest impact a chemist can have on the economic and environmental performance of a manufacturing process is in selecting the optimum synthetic route using the best available techniques/technologies at that moment in time. Route selection is a complex process, and synthetic routes can change during the development pipeline of an API, and post launch as part of life cycle management activity. In their paper ‘Critical Assessment of Pharmaceutical Processes; A Rationale for Changing the Synthetic Route’  Butters et al. published their work on the ‘SELECT’ criteria which have since been widely adopted . A manufacturing route could be improved/ changed to meet any or all of the SELECT criteria.
The SELECT criteria are covered in more detail in Introduction to Process Chemistry in the Foundation topic.