If you want a transaction to be recorded in a general ledger account then both the segments of a general ledger master i.e. chart of accounts segment and company code specific segment needs to be defined. You can not do transaction posting to a general ledger a/c if company code segment of that particular GL a/c is not defined.
In a chart of account, account group is used to organize and manage a large number of general ledger a/cs. When you want to create a general ledger a/c master data by using transaction code FS00, you need to select the a/c group in the chart of accounts segment of the general ledger a/c master.
If you assigned more than one general ledger account to an account group then those GL accounts will have same functions and are assigned to a particular number range. The account group controls the fields of company code segments of general ledger master. The field status group maintained through account groups manages which fields are required entries, which fields are optional entries and which filed are required for display.
While defining an account group for a company code, you need to first understand the requirements of a business and then the groupings can be done based on the business requirement. As we discussed above, by groupings you can manage the fields of the general ledger accounts defined under the group, the number range of general ledger accounts and the type of accounts in chart of accounts segment.
Account group helps a lot in managing the general ledger master date creation.