What's really bad is food past the "sell by date" and food left over in a buffet.
My stepdad sells snack cakes, and the ones that don't get sold by the sell by date, he has to take back. Now, these are all still perfectly edible (not really healthy, but still), and he has to toss them out. Most of the time he takes them to a Day Old store, where they sell the stuff discounted, but sometimes he waits too long and it ends up in our garage, waiting to be tossed out (needless to say, my friends and their siblings have a nice little stockpile of "expired" snack cakes that would have otherwise been thrown away despite being edible).
On a separate but related note, one time, my friends and I went to a Pizza buffet around closing time. The manager came out (we were the only ones left in shop) and gave us each some cardboard pizza boxes to take home the left over pizza, which he would have had to throw away anyway, but had been cooked at most a half hour earlier. We had lots of pizza for the next few days.
There's also people who toss out leftovers instead of saving them. This is why my grandfather liked my mom more than my uncle's wife, since my mom kept leftovers for the next day (my Aunt would toss them).