Interesting question - let me try to answer with a little more background information.
In general Posting Groups are used to create links between the different application areas such as Customers, Vendors, Item, Resources, Fixed Assets and the General Ledger application area.
Posting Groups are used to find the right G/L Accounts.
For more information see msdn.microsoft.com/.../hh168345(v=nav.90).aspx
But that doesn’t explain what we need the Posting Groups for in the G/L Accounts itself.
If you enter a G/L Account directly into a journal of course you don’t need any logic to find this G/L account! You just enter the number directly. There is no “direct” impact on the accounting!
But in case you want / have to work with VAT (like in all European country versions) you need at least the following Posting Groups in the G/L Journal Line:
- VAT Business Posting Group
- VAT Product Posting Groups
in combination with
- Posting Type (Sale / Purchase)
These three parameters control the VAT handling, such as VAT percentage, G/L Accounts for the VAT Amount, etc.
(More details about the VAT setup can be found in the help mentioned earlier.)
You can enter the VAT Posting Groups manually in the G/L Journal Line, but you can also set up these Posting Groups and the Posting Type in the G/L Accounts and then get these fields prepopulated in the G/L Journal Line.
The values can still be changed if needed.
That makes it easier for you to get all the needed information entered in the G/L Journal Line and ’s the main reason for having the VAT Posting Groups in the G/L Accounts.
And then there are still the "General Business Posting Group" and the "General Product Posting Group".
These General Posting Groups are not needed for VAT.
But there are use-cases for these two parameters too (Remark: you cannot use these two parameters without using the "Posting Type" also).
In Journals:
Imagine you register a sales invoice through a Sales Journal or through a General Journal and you want to allow the customer to deduct Payment Discount if they pay the invoice in a certain time frame.
In this case it makes a difference whether or not you used the General Posting Groups in the journal (the Posting Groups on the G/L Accounts are just for pre-population)!
The difference is where NAV checks for the Payment Discount G/L Account. If you didn’t use the General Posting Groups when posting the sales invoice through the journal then the Payment Discount G/L Account is taken from the Customer Posting Group. And if you used the General Posting Groups when posting the sales invoice through the journal then the Payment Discount G/L Account is taken from the General Posting Setup.
(The second options offers a little more flexibility, if needed. In some countries this is even mandatory)
In Documents (for example Sales Invoice, Purchase Invoice, etc.):
As mentioned in the help …
If you use an Item the Posting Groups (from the customer/vendor and from the item) are used to determine the G/L Account (indirectly).
There is a check with the posting routines that you have to use Posting Groups if you register a transaction through a sales/purchase document.
And now … if you want to use a G/L Account directly in a document … the same check for Posting Groups is done within the posting routines. This means that the Posting Group field has to be filled for all lines in a document (except lines of Type = Blank/Text).
If you would not use a Posting Group for a G/L Account Line the following error message is thrown:
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Gen. Prod. Posting Group must have a value in Sales Line: Document Type=Invoice, Document No.=xxxx, Line No.=yyyyy. It cannot be zero or empty.
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And therefore it makes sense to enter the default Posting Groups in the G/L Account and get it pre-populated when the G/L Account is used in a document.
Hope this helps
Dirk
