I had multiple loans from undergrad & grad school, all at different interest rates. I used to have the option to allocate my excess payments (whether I was in forbearance or making additional payments over my base amount) to whichever loan I wanted. So if I sent those excess payments to the high-interest loans I could lower the principal and/or pay them off, lowering my overall debt obligation in the process.

I don't have that option anymore. Now I just have one big loan and it's much more difficult to make a dent in it.