When you use relationships, you can use a dropdown and select the value to show and the real value writing on the tables which is good but when working with a lot of data, we might need to see more than 2 display fields to match the option we are looking for. For example, if I have a Doctors list, chances are that I have the same doctor's name for more than 1 record, it'd be good if besides the doctor's name as displayed value, we could also have the address field. Like working in MS Access, you can choose how many columns you want to display for the dropdown and set the primary column as that's the value stored in the database.
SABA Test commented
see also this Idea box request - seems similar
Bethany J. commented
A temporary solution that might work for you is to create a Virtual field that looks up the doctors' names, then make your real field cascade off of the Virtual one, with the display value set to the address while the true value remains whatever you need it to be for the database.