In MIGO, when the components are exploded , and then you do Batch determination, and there is less stock in the batch(say 20KG) as compared to that maintained in the BOM (say 30KG), then the batch determination still returns the quantity of 20KG , and this can still be posted.
There is a SAP Note (i dont remember the note number) which tells us to activate an Error message for Batch determination, in that case, if the Batch determination returns a smaller qty than the actual required qty, the batch determination fails with an error message .
One more issue you can face is that the Users are allowed to manually adjust the Component qty in MIGO , this can somewhat be controlled by " fixing" the component qty in the BOM or subcon PO .(this however can be an issue if you work with partial receipts ).