I noticed a website used the product schema type to mark up their product and used more than 1 description.
Is this a bad thing? Are there any benefits from this?
I don't think will have any impact. In fact, if they state two descriptions without using an array, then I believe that Google will only read the final description (if you test it the structured data testing tool, it will only highlight the final description stated), so I don't think there is much point.At least that is the case for the JSON-LD format.