Canceling an Order releases all of the Items so they are available for other Rental Orders during that timeframe.
We suggest that you Cancel Orders rather than delete them so you can even keep track of Proposals that don't lead to confirmations.
If you delete an Order, you will no longer have a record of it. It will be as if it never existed. But with Canceled Orders, you can see what Items are being asked for but not booking, how many Proposals you create for every Confirmed Order, and other metrics that can help you make better decisions about your rental business.