Middleware CRM 5.0 with R/3

Hi gurus;

I'm trying create a middleware to connect CRM 5.0 and R/3. In a document to Sap Best Practice "C71_BB_ConfigGuide_EN_US.doc" say that is necessary create a connection RFC between CRM client 100 and CRM client 000.

Do you think is necesary create this connection? If this connection is necesary, what's the target of this connection?

Thanks.

Regards Miguel.