In the Legacy UI, User IDs did not have to be email addresses. This meant that you could create a user for "Automation" that would allow for API usage that was not dependent on an employee staying with the company. When an employee leaves, the API no longer functions. Additionally, by forcing email address as the ID, when a user has an email change (marriage, Divorce, company email changes, a new user ID must be created to accommodate. This means ALL of a users reports are now orphaned AND can not be seen/used/structured by said user. This issue also causes an issue in problem solving. As an Admin, when a user experienced an issue in the Legacy UI, I could create a user with the same access as the one with the issue and reproduce the error so I could solve the issue. Now, unless I create a user with me PERSONL email address (which most companies would not be a fan of) I either need to ask the user for their user/name/password (never a good option) or try to watch their screen and then still not be able to reproduce the issue myself to troubleshoot.