SD module is highly integrated with the other modules in SAP.

Sales Order – Integration Points Module
•Availability Check - MM
•Credit Check - FI
•Costing - CO/ MM
•Tax Determination - FI
•Transfer of Requirements - PP/ MM

Delivery & Goods Issue – Integration Points Module
•Availability Check - MM
•Credit Check - FI
•Reduces stock - MM
•Reduces Inventory $ - FI/ CO
•Requirement Eliminated - PP/ MM

Billing -Integration Points Module
•Debit A/R - FI/ CO
•Credit Revenue - FI/ CO
•Updates G/ L - FI/ CO
(Tax, discounts, surcharges, etc.)
•Milestone Billing - PS

Return Delivery & Credit Memo -Integration Points Module
•Increases Inventory - MM
•Updates G/ L - FI
•Credit Memo - FI
•Adjustment to A/R - FI
•Reduces Revenue - FI