Update Snapshot Qty - Stock Count Authorization

Could someone explain what exactly "Update Snapshot Qty' button on stock count authorization screen does.

The sample scenario:

Unit and Amount count was scheduled and executed on Monday. Snapshot was taken just before the stock take  on Monday.

Now count s being authorized few days later lets's say Friday. in SIM on count authorization screen we have a button 'Update Snapshot Qty' . What is actually updated in the snapshot qty , and how the end result would be different with and without using 'updating snapshot qty' prior to authorization ?

Thanks for your input