This is an enhancement for CRM Online (and On-Premise), but there is no option for this in the Product Version drop-down list.
The enhancement request is for CRM Administrators/Developers to have the ability to view the entire CRM site as another user's role. Often times we are building out Security Roles, Business Units, Forms, etc. and need to ensure the end user is seeing, accessing, and function as intended for their work and role.
The enhancement would have a "View As" option for Admins/Developers and then and option to pick a Security Role (or a combination of Roles). Once these are selected, then a "Start Viewing" option to start the session. This will allow us to "play" that person's role, navigate, run reports, create Views, lookup records, etc. as the person. The limitation I would see is the ability to Create, Update, or Delete (CRUD) records. This should be left to the person needing to perform their tasks.