Assigning collaborators to an issue or pull request helps clarify responsibility and ownership. When multiple collaborators are assigned, GitHub does not limit responsibility to only the first assignee.
Instead, all assigned users are associated with the work item and can receive notifications based on their notification settings. This is useful when several people share responsibility for investigation, implementation, review, or follow-up. Assignment does not automatically lock the issue or pull request, and it does not automatically change the item's status to "In Progress." Status tracking is usually handled through labels, Projects fields, or workflow automation. In GitHub collaboration workflows, assignees make it clear who is expected to work on or respond to an issue or pull request.