GL Account field in MB1A GOODS ISSUE WITH MOVEMENT TYPE 201

Hi

I am using the movement type 201 with MB1A transaction code i.e goods issue.

During goods issue we have maintained the Material code say X.

Through OBYC settings system pass the following entry-

                                                  Consumption A/c Dr

                                                       To RM     A/c.

What is the additional  purpose of GL Account field in this screen even though system determines GL accounts automatically.

Thanks.

Srikanth.