Hi,
As you aware FI is core and integrated with other modules, The answer is with your question itslef, integration is depends upon how do you want to extensively utilise SAP for your business process.
INPUT-->PROCESS-->OUTPUT
Input = Man (HR module), Machine & Method (PP module),Material (MM),Money (FI)
Process = Manufacturing or Service
Output = Product (Sale = SD Module) or Service (Service Mgt)
Regards,
BK