Generally sort key allows you to configure what to populate in assignment field for FI documents. ( Refer assignment field in reports FBL3N , FBL1N, FBL5N) , you can enter sorting key in Vendor and customer accounting data , and control data of GL account. Assignment field is generally used to run automatic clearing of open items you can configure it here:
SPRO -->Financial Accounting --> General Ledger Accounting -->G/L Accounts--> Line Items -->Display Line Items -->Determine Standard Sorting for Line Items
Sort Key Functionalities ---- http://scn.sap.com/docs/DOC-35136
Sort Key Functionalities (Vendor Master and Customer Master )
原文：http://www.cnblogs.com/jefflu2012/p/4332892.html