Benefits
Drupal developers get major benefits and significant drawbacks with the multisite feature.
The main benefit is consistent governance to help manage sites at scale. Imagine having to manage hundreds or even thousands of similar Drupal applications. Performing code updates site by site would be extremely laborious.
Another benefit is growth. New sites can be added at any point and they can build off of the existing systems and code implemented. Practices established for leveraging multisite can readily be extended to more sites.