USC SCA letters of rec?

I’m applying to USC’s School of Cinematic Arts. USC asks for 3 letters of rec that you can submit either via Slideroom or via the Common App. Is using one better than the other? Is it ok to submit more than 3 letters? Thank you.

Common App seems to be the more common of the two. As regards the number, just stick with what is required. Some universities look at the applicant’s ability to follow instructions no matter how simple.