Rule Definition
How you define numeric fields can have an impact on performance. If you are using a field for arithmetic increment or as a subscript and the field has 8 or fewer digits it is quite often best to define it as a binary number (usage is BINARY, COMP or COMP-4) that is signed. This is because binary numbers can be manipulated much faster and consume less CPU.

Remediation
Check declaration of variables used as subscripts or iterators and add a sign in their picture, adapt the number of digit to 4 or 8, and set BINARY in their usage clause.

Violation Code Sample

01 DIRECT-TAX-RATE. 
01 I PIC 9(01).
02 TAX-RATE PIC 99 OCCURS 5 TIMES INDEXED BY TX-INDEX. 
...
PROCEDURE DIVISION. 
PERFORM VARYING I FROM 1 BY 1 UNTIL I > 6
... 
END-PERFORM.

Fixed Code Sample

01 DIRECT-TAX-RATE. 
01 I PIC 9(01) USAGE BINARY.
02 TAX-RATE PIC 99 OCCURS 5 TIMES INDEXED BY TX-INDEX. 
...
PROCEDURE DIVISION. 
PERFORM VARYING I FROM 1 BY 1 UNTIL I > 6
... 
END-PERFORM.

IBM Cobol - Best Practices and Recommendations