1. In SAP you will always get integration with other modules.
SD will interact with FI,
MM will interact with SD :-
1a. Looking at MM and SD interaction first, take the scenario of a
third party order process.
This process uses a PO (which is sent to your vendor)
Also invoice verification is used further along the process to check
that the invoice you send to your customer is the same material
and quantity as that which the vendor sends to you
(but obviously shipped directly to your customer).