I agree with Rod that this is printer's waste.
You quite often see Spanish examples like this from this period.
If you google for images with "Spain printer's waste" you should see many examples of stamps like this.
If you were running a test print to check the setup of your printer why not use an old test print that was lying around rather than wasting a new sheet of paper?
In my view it's collectable but not valuable. You can see similar examples on eBay