DSB or SSB, been using them both for 30+ years. I have found NOT vacuuming a DSB eventually leads to failed biological action due to stagnation. It may take years but it will happen IME. I no longer use a DSB in the DT but moved it to the refugium, much easier to maintain in a healthy state. This is GROSS but compare it to NEVER flushing your toilet. Well, what you find in your sand bed, regardless of depth, is poop from all your critters whether fish, coral, crabs, snails, feather dusters, whatever. They eat, they poop, the sand bed gets dirty. Some will say, yeah but that’s why I got a big CUC to take care of the pollution. Guess what? They eat, they poop too. Syphoning portions of your sand bed whether DSB or SSB helps keep it clean, like flushing the toilet! Do it with every water change. Your entire system will benefit from it.
Dick