Having heard a number of auditions over the past couple of weeks, I am reminded of a very under rehearsed part of the audition - saying the name of your piece, pronounced correctly, and the correct name of the composer. I have heard some real problems with this, and while you might not think that this could play a big part in the outcome of an audition, but it could. If every part of an audition is roughly equal, it could possibly tip the balance.......why take a chance - be prepared.
An while on that subject - know the name of the character singing the aria! I will, and some other judges will ask for piece by saying something like "let's hear the Posa" (Don Carlo). I have seen more than a few blank stares when I or another judge ask for a piece in that manner.
So, prepare every part of your audition - you never know what will be the difference maker!