If you Void the check in Check Reconciliation, the invoice will remain posted and paid.

If you Reverse the check in Check Reconciliation, the invoice will become un-paid, and all relevant GL transactions to back the payment out of the bank account will be performed. Unless there is a really good reason to Void the check, you really should use the Reverse function to cancel the check.

There is an option in the AP company profile to remove the Void option from the Check Reconciliation function, so that you don't choose this by accident instead of Reverse.