USE CASE :_

[purnendu]

USE CASE :- Create one field that is list data type and  give reference of any  type(ex :- sys_user) then when someone remove any value from that field and whenever some one added any value for that field then it will give us popup with added user and removed user.

How can we achieve it???

[Mark Manders]

This is not a use case, this is a solution you think is the best way of resolving something.

What is it you are looking for? What is the business case/actual requirement? If you need to know which user was removed or added, why not just add it to the record activity?