If you meet all of the conditions for the voucher +10% (and there are a lot of them - eg. no previous changes by either party, no ticket reissues, booked online, not a Lite fare, didn't book with a previous voucher, etc, etc), it can be a nice bonus. But you can only spend it at QR, including any residual.

If you do not meet all of the conditions, then your cancellation will be treated as a voluntary change and the penalties in the fare rules of the ticket will be deducted. Then you have a voucher of lower value that you can only use on QR. Under those circumstances it is probably more flexible to take a cash refund for the same amount.

As always, be sure to read the full T&C small print before deciding...

https://www.qatarairways.com/en/trav...her.html#Terms