Have you wanted to keep track of logins to your database?  A logon trigger can help you easily keep track of this information.  This is a database-level trigger and fires after logon.  For my purposes I only want to keep track of true user processes; no background processes and no process running under the Oracle OS user.  The underlying SQL I used to obtain login information is limited to session type USER (not BACKGROUND) and OS users other than the oracle account.  If your database runs under a different OS user and you don’t want to keep track of these logins you can change that value to the AD or other local account.

There are several reasons that having access to this login history can be useful such as auditing requirements.  This can also be useful for identifying who is using which SQL logins.  This is also helpful to identify what types of applications and servers are hitting your database that may impact performance.