Pull-Requests are a mechanism to notify others about changes to a branch that you want to merge. It is often used in combination with trunk-based development, where you let your teammates know that your changes are ready to be merged into the trunk. Open-source software (OSS) uses this mechanism too because the requester usually does not have permission to merge directly.

But Pull-Requests are more than a notification mechanism. They can raise awareness in the team about some specific feature, spread knowledge between teammates, and even exercise control over what is merged. It is a mechanism for collaboration.

However, to make this collaboration work, you need someone to review your Pull-Requests. In OSS, this person tends to be the codebase owner, and yet it could take them days or months to review your changelist. In the corporate world, where teams are of different sizes, things could get more complicated to find the right person for review.