Flow of down payment

Dear

i understood all steps regarding Down payment processing by this link http://scn.sap.com/thread/810960 Thanks to them

But where i confused is

now do the cycle    OR - LF - FAZ (billing doc type)

Generally we create invoice to customer erliar so but here they have mentioned the flow is as usewell

so plz tell me after creating all settings for down payment processing Diractly we can create the billing or we have to fallow this steps OR - LF - FAZ (billing doc type)

But we are doing like this what is use of down payment bz created order, delivery, and then biling

plz let me know

thanks a lot