In Drupal 7, hook_update()/hook_install() were well-established mechanisms for manipulating the database when installing a new site or updating an existing one. Most of these routines ended up directly running SQL against the database, where all kinds of state, configuration, and content data lived. This worked reasonably well if you were careful and had a good knowledge of how the database schema fit together, but things tended to get complicated.
With the maturing of Features module, we were able to move some of this into configuration settings via the ctools-style export files, making the drush feature-revert command part of standard workflow for deploying new features and updates to an existing site.
Aegir is often seen as a stand-alone application lifecycle management (ALM) system for hosting and managing Drupal sites. In the enterprise context, however, it’s necessary to provide mutiple deployment environments for quality assurance (QA), development or other purposes. Aegir trivializes this process by allowing sites to easily be copied from one environment to another in a point-and-click fashion from the Web front-end, eliminating the need for command-line DevOps tasks, which it was designed to do.
Have you been looking for a self-hosted solution for hosting and managing Drupal sites? Would you like be able able to upgrade all of your sites at once with a single button click? Are you tired of dealing with all of the proprietary Drupal hosting providers that won’t let you customize your set-up? Wouldn’t it be nice if all of your sites had free automatically-updating HTTPS certificates? You probably know that Aegir can do all of this, but it’s now trivial to set up a temporary trial instance to see how it works.