Imagine you’d just finished a great first date. Lots in common, easy conversation where you really got to know each other, with all signs pointing to a mutual interest.
Would you end the date by saying,
“By the way here’s another story about me (one that’s not interesting or witty or even all that important to me)?”
No. There’s no reason to add uninteresting onto what’s been interesting. Far better to end on a high note.
Think of the “Additional Information” sections of your college applications the same way. If there’s something worth sharing, something that’s important to you or that you feel the admissions office should know, and that information could not fit in the rest of the application, by all means, add it.
But if it’s not all that important, if your proudest accomplishments have all been shared, if you wouldn’t have even thought to include it unless the additional space was offered, leave it out.
Nobody ever hurt their chances of admission (or a second date) by ending on a high note.