ALM is a cycle and there is no part which is more significant then the other, but putting that aside deployment is the dangerous part of all. Deployment means moving your build to other environments and making it work. In web site deployment it means setting up pool if needed and adding the correct config files. In Software it means sometimes uninstalling the previous version prier to installing, but the main idea is to have the deployment do the same process in a control environments and it does not matter if it’s Dev, Test or Prod.
Albert Einstein once said “Insanity: doing the same thing over and over again and expecting different results.” and this is why automated deployment is so impotent. One can get a high confidence that if everything is configured and nobody tempered manually a deployment process which works in Test will also work in Production.