then, if the 'house allowance' is QR 20,000 and you only spend QR 16,000, you just cash in the QR 4,000 without any problem?

If that is so, then I was thinking this allowance stuff wrongly. I though you were bound to spend the allowance money in the allowance subject, otherwise you loose that allowance.
I have not seen anywhere a clear explanation of the whole allowance concept.

Please confirm/correct me if my interpretation is right/wrong.