[dba-SQLServer] Single User Name for SQL Server Login?

I was talking to a SQL DBA today at one of my customers.  She suggested that
I use a single username and password for all of the client PC's (about 200).
I'm going to ask her about why we should do this in more detail later.  I'm
setting up this BE with Windows Authentication.

She threw me for a loop - why do this?  Is this a standard practice in some
situation?  My app at this customer has an entire virtual server and the
entire SQL instance is for just this app.

Thanks!
Dan