Aspen has the ability to masquerade as other patrons, which is extremely helpful in troubleshooting. It would be great if Koha could give at least superlibrarians the ability to masquerade as other staff to troubleshoot their permissions and such. As is, we have to either know their password or have them sitting next to us in order to troubleshoot things. This would be a big help. Of course, Koha would have to be able to log this behavior properly.
This type of feature is often called "Impersonate"/"Impersonation" in other systems. There have been times where I've thought it would be useful for troubleshooting certain problems. I think it would need to be a controlled by a configuration option in koha-conf.xml and be limited to superlibrarians at least.