What is the difference between on-account and unapplied receipts?

This is the answer I got from Metalink but fundamentally it sound the same to me?  Can anyone tell me the difference between the 2 and when to use what?  Thanks.

What is the difference between on-account and unapplied receipts?

Unapplied Receipt:
This receipt is not applied to an existing invoice when it is entered. When
the customer does not want to apply the entered receipt they can leave it as
unapplied and apply the amount on a later date.

On-Account:
In case of an On-Account receipt, there is no identified invoice against the
receipt. Advance money is received from the customer and the invoice for the