Sign In History can be useful to see when user's last signed in, or if a user is reporting having trouble signing in, this could tell you what the problem may be.
To view a user's Sign In History:
1.) Start from your Core persona. 2.) Navigate to Users > Edit User Profile Data. 3.) Search/select the user you would like to view Sign In History for. 4.) Once on their profile, scroll down to Sign In Information on the left. 5.) Click the View Sign In History link.
This will allow you to view sign in information, such as successful logins, incorrect password attempts, if the user was locked out, and date/time/IP address information.