ms access – Unique Records property in the delete request

In Microsoft Access, if you create a delete query based on two or more linked tables, you must open the property sheet and set the Unique Records property to "Yes." If you leave it on "No", you get the error message "Unable to delete specified tables".

Now, I know how to make the delete request work (by changing the Unique Records property). What I do not understand, it is Why. Why should this property be set to "Yes"? What does this change in the delete request? What problem is caused by leaving "No"? If you could explain why setting up this process is necessary, I would greatly appreciate it.

Thank you.