Chapter 1, Proxmox VE Fundamentals, introduced GNU/Linux containers generally and worked particularly at distinguishing them from virtual machines. This section elaborates some advantages of containers, and it imagines a scenario ideal for container deployment.
Where an administrator could run 10-100 virtual machines on a physical host, she/he could run 100-1000 containers on the same host without compromising significantly on performance (http://computerpcdeal.com/servers-dell-poweredge/news_2014-06-17-05-30-07-224.html).
Containers may be thought of, initially, as very lightweight virtual machines, but with much lower overhead and the added value of simplified deployment.