Receiver Determination in BPM

Hey,

Can anyone Explain me the significance of the reciever determination step in BPM.

What i did is created a receiver type container variable.

Used it in Receiver determination step.

In the send step that is following the receiver determination step, The "Reciever From" is Set to reciever List.

The List is Empty.

In the Configuration i have to define the receiver Determination.

At runtime, when i check the receiver List it is populated with the Service mentioned in the receiver determination(in configuration)

My question is what is the significance of the receiver determination in BPM when the purpose is satisfied by the receiver determination in ID.