It annoys me when my computer (or, even more, someone else’s computer) makes a gratuitous noise upon startup.
While I know that, on my Mac, I can avoid the sound by either muting before shutdown or holding down the mute button while starting it up, I often forget. And I am especially prone to forgetting when it’s most important that the computer be quiet.
It’s nice and easy. Here are the scripts I use; the instructions are in the comments at the top of each file.