> Considering that I'm a junior in high school, I receive a substantial amount of college-related junk mail (between five and ten pieces per day), in addition to perhaps three other items. I don't understand why it is preferable to sort though my mail digitally.

Well, wait until you have a power bill, water bill, gas bill, garbage bill, phone bill, cable bill, mortgage, credit card bills, car note, doctor's bills, lab results, dentist's bills, vet bills, student loan bills, newsletters from your kids' schools, bank statements, ...

Some of those need a response, some don't because you've already set up automatic bill payment, some are information you want and can then discard, some are things you need to keep for your records.