An engineering change order is very important to keep track of any change to the initial proposal and product part especially when you don’t have a locked BOM list. sometimes your dependant on parts suppliers roadmap and end off live notice. Also, sometimes you can not depend on one vendor or supplier and must qualify more that one. ECO documents help for manufacturing, mass production, even troubleshooting and, failure analysis after deployment. it is very important to keep track and constantly update of PCN and EOL for parts used for your product. from my experience, it always helps PM to better manage the projects.