Impersonating a user is not the same as "ghosting." When you are impersonating a user, you are logged in to their account, and any activities you complete (such as questions and tests) will be saved to that account. Be careful to look, but not touch and always click on the "x" when you are finished.
Impersonation allows you, as an admin, to see exactly what the user is seeing on their end. If a user is saying that a part of their course is not loading, you have the ability to see if this problem is a course-wide problem or a special case that has to do with their system configuration.
Impersonation allows you to see if a problem is actually there or if a user's browser is possibly causing the problem!