It de-nastifies the black tank (if that is really possible I don't know). But consider you are dumping very soapy water into the tank. You don't have to worry about the "pyramid" under the toilet.
On the downside, of course, it could fill the black tank a little bit quicker.
HOWEVER, the only way I could see this as a problem is if you were boondocking. But I simply can't imagine doing laundry boondocking (would have to run genny whole time). Otherwise, we usually have hookups.
Full timers would most likely always try to be on sewer anyway.