When this option is checked, this project will be equipped with UI for creating "feature branches", which are branches for changes eventually targeted for integration into this project, and accepting changes from such feature branches (by means of svn merge in Subversion 1.5.)

Hudson allows automated and/or manually-triggered integrations, tracking around what changes from which feature branches are integrated when, and other useful data collection around this.

This mechanism is useful for keeping a large project stable, because the trunk of the development is shielded from problems in feature branches, and integration can be done much later after a build, after you qualified it through testing.