In terms of rollout it's more like releasing new drugs - initially it's very small groups that will be tightly studied, over time these groups are increased in size (and monitoring is probably reduced in scope).
The use of feature flags to control rollout and "blast damage" from unexpected behaviour or bugs is really useful. Let me give a real example I was involved with - mobile app development.
You can never test everything (not every Android phone variant, nor every 3rd party app which may interfere). Being able to roll out a new feature gradually and then revert (or in our case even blacklist certain models) is key to increasing quality and reducing problems. It also accelerates development and (in my mind a _key_ benefit) reduces stress/anxiety for the developers.