In my economics 101 class, i heard rationing is bad when an item is oversupplied. Why?

But Argentina has a beef heaven though. Why is oversupplying necessaeily a bad thing even if you have to throw away some unsold beefs that went bad? I am not saying all items should be oversupplied, just a few cruicial items for the quality of life like beef. I asked this to my TA too, but i am probably gonna get an answer here faster.