clarification neded on extended RCVR Determination

Hi Experts,

Plz clarify me here:

1.we can send mesages to multiple receivers based on condition in conditional editor......when exactly we should go for extended rcvr determination?

2.why we need to use a seperate mapping for extended rcvr determination using basis object"receiver determination"? wat is the use of this mapping?

3.do we need to go for enhanced interface face determination everytime when we r gong for extended rcvr determination?

4.Plz let me know what is the sequence of processing steps that takes place in IE/IS...

Thaks in advance.