Uber developed Piranha to seamlessly delete code related to obsolete feature flags, leading to improved developer productivity and a cleaner codebase. At Uber, we use feature flags to customize our mobile app execution, serving different features to different sets of users. These flags allow us to, for example, localize the user’s experience in different regions where we operate and, more importantly, to gradually roll-out features to our users and experiment with different variations of the same functionality.
Source: uber.com