Sometimes we need to restrict requests based on the group of the user that has the item currently borrowed, not only the group of the user that is trying to request.

This is particularly useful when you have items loaned to a user for an specific loan period (sometimes even for months or years) and you want to avoid users to request that item loaned to that specific user group but allow them to request items currently loaned to other user groups.

Take teachers and students for an example. You would like students to be able to request items currently loaned by other students, but not the ones currently loaned by teachers.