I would worry that as it is using the same database, that if the copied tables of the sandbox were to get corrupted while testing, that the entire database might corrupted as well. Yeah, having a backup is good, but if it's a particularly large database, say in the GB range, restoration can be quite time consuming if restoring from an offsite backup. Having gone through something like that with a cloud hosting situation, I'd have to say I'll pass on it for any production website that has a database of around 200MiB or more in size. I can see the appeal for a small established website or a startup to test different iterations quickly.