[Avodah] What am I missing?

[Ben Waxman via Avodah]

Re prozbul, I seem to be missing something. Personally I haven't loaned 
out any huge sums such that if I don't get them back, I would  be 
reticent about loaning in the future. If I did loan out something small, 
why should I sign the prozbul?

If the borrower doesn't pay me, well he doesn't have to (right?).
If the borrower does pay me, he gets a bracha and everyone is a winner.

What am I missing?

Ben