- There are large scale SAP or Peoplesoft Installs.
- There are medium scale installs such as critical updates to the server and/or desktops.
- There are small scale desktop application installs.
All of which have various degrees of trip points in which failure can occur.
The bigger the project, the more people, the harder it is to manage and the more points of failure are exposed.
That is why SAP type deployments take years to roll out and it only takes a few minutes for me to update my web page. These are the same concepts but way different scales.