Plain Old WebContainer are overly bloated, complicated and cumbersome to use. The Java WARs are often bigger than whole server installations. Deployments takes longer than necessary. Monitoring capabilities are rather limited as applications in production are a “blind flight”.
Java EE containers are the lightweight alternative to bloated, complex and hard to manage WebContainers. This video explains why, with few slides and some code.
Video producer: http://geecon.org/