What is the origin of the idiom "be my guest" and when to use it?

The idiom "be my guest" is a polite and accommodating expression used to grant permission or give someone approval to do something. It is often used when one person is inviting or allowing another person to take a particular action. While the exact historical origin of this idiom is not precisely documented, it is a widely recognized and commonly used phrase to convey willingness to allow or support someone's request.