iNetSudo for SugarCRM 8.0+ and 9.0+ allows SugarCRM Administrators to easily change to a different user without knowing their password, enabling them to configure and test any user's experience.
Other add-ons of interest
OneClick Sudo Login for SugarCRM 8 / 9
Sudo Login (or Masquerade) allows Administrators to log in as any regular user without asking for their password and without disconnecting them. Specially useful for configuring their workspace (filters, reports, dashboard) or to support users (reproduce issues, help them step by step, etc).