prepayment on invoice check box in AP 11i

Hello Experts.

1)In 11i we need the information on what is the use of prepayment on invoice check box in invocie distribution.
2)while appliing the invoice with prepayment we are having the option to apply or prepayment on invoice option.
we need the inforation what are all the differences uses on this and any impact on the accounting/GL.

Thanks in Advance.

Regards,
Preetham