Deleting an invoice involves removing it from the system and this operation cannot be undone. Here’s more information on how you can delete an invoice.

Voiding an invoice marks the invoice status to Void and it will be available in the system. This is an irreversible action as well. Here's more on when you would typically void an invoice. 

Generally, to ensure clean accounts it is advisable to void an unwanted invoice rather than deleting it.