Hi,
The purpose of CPLTD is exactly for requirements to split the same loan with the short term part and long term part and treat them separately. But when there is an accounting requirement to treat the current portion and long term portion separately, then there is a need to have 2 different valuation classes short term and long term liabilitites in the valuation area following that accounting principle.
In cases of other accounting principles which does not require to split the current portion, there can be a common valuation class as liabilities. And as you said, AAR is used for posting to different accounts and it only makes sense to have valuation class specific for valuation area as a parameter rather than General valaution class as a parameter which is common for all valuaiton areas.
As you pointed out, The combination of valuation area and general valuation class is unique and it is for this unique combination which requires separate accounting that we create valuation classes.
Regards,
Ravi