I am not an accountant, so take what I write with a grain of salt.
Tax-wise, they do not make any difference, but accounting-wise in terms of credit control and customer management, it makes a huge difference.
Generally I would advise against deleting invoices - they are never really deleted in the system for audit purposes, and if you ever get audited, deleted invoices will raise questions.
A “bad debt” has a different purpose than a credit note; bad debt insinuates that you were unable to collect the monies owed, pointing to a “bad customer”, e.g. unwilling to pay, so someone you probably want to avoid in the future.
A “credit note” on the other hand, indicates you are either refunding the client, or voluntarily relinquish the outstanding amount for some valid reasons (I’d give those in the comments on the credit note).