I would disagree to a certain extent. I have a large 300 gallon display and had a pair of them in my tank for a couple of years. I lost the female at some point after a couple of years to what I believe was a tunnel collapse as she was excavating and holing herself up. The male lived on for about a year as I tried to replace his mate but never took to any of them.
They did dump a lot of sand in my tank which was a problem for the first few months, but after the bed matured it sank down to the bottom. For me, it was no worse than the large tangs I have that feed off the food settled to the bottom and then later on poop it out as they swim in the water column. The sand from the gobies was isolated to the bottom 6-8" of the tank as they rarely if ever went above the bottom 1' of the water column, more often than not sticking to the bottom 6".
As for life in my sand bed, they kept it super white and there was some life in there. It wasn't what I have now that they're gone, but my sand bed also does not look as nice as it did before. I've got a 2-4" bed throughout the tank and plenty of life in other areas of the tank. Right now, though, my sand has multiple worm chimneys and looks a bit dingy. I've been on the lookout for a good pair for the past couple of years to replace them and clean up my sand again.