When did the VendTransOpen record created? and what is the usage?

Hi, Experts:

Can anyone tell me when the VendTransOpen record created?

I realize The VendTrans table contains posted transaction information for the vendor.

and the SpecTrans  contains records that marked for the settlement, and Records are deleted after they are posted.

So after ledgerJournalTrans marked some records for settlement. these records will insert into specTrans.

After posting , it will create records in VendTrans. and delete records in specTrans.  so what is the usage of VendTransOpens table and when it is inserted records?

 thanks