If you have a residential property that's just closed and is not rented out and not used (even seasonally, such as a vacation home), it's not giving any worth towards the society it exists in. It's only fair that the owner pays higher taxes over it to help fund the creation of new housing for the existing demand.
I don't really think just occupying it is a great idea, but I do think it might force the owner to employ the property in a more socially responsible way.