We would like the ability for administrator users to be able to log in as any individual user. There are multiple benefits such as being able to view exactly what an end user is seeing and making changes to assist them. As well as to check security and access.
Currently, when we need to check the access an account has (checking that the restrictions we have in place are providing us with the desired result), we will typically clone a user account and log in to it. We also have a few test accounts setup for each our groups for this. Having the ability to log directly into a user account would be helpful.
As an example, Concur has this ability, it is called "Acting as Others".