This is one of the new improvement in Financial management -Chart of Account
Now one can define categories and subcategories in chart of account itself . This feature is useful for reporting purpose as well as categorization of ledgers.
Straight from MS :
We have added account categories and sub categories so you can group general ledger accounts to fit your need for financial reporting. For each G/L account, you can specify the account category so that ledger entries posted to this account are categorized as assets or liabilities, for example., or an income or an expense, and so on.For each account category, you can choose between different sub-categories. You can also create new sub-categories to fit your need. For example, for the G/L account category Income, you can define as many sub-categories as you need so that you can differentiate between income from services and income from product sales.
I loved this feature as in initial version we have to add these as custom field and prepare reporting based on the same ( Specially in Indian version)