having a deep sandbed anywhere other than the display is the pro
its detritus prefiltered ideally when setup outside of the dt, then they can actually have a chance of working to reduce nitrate when its not impacted by whole waste pellets all day long. it must be said that getting a sandbed to perform measurable nitrate reduction varies, even if someone sets up ten tanks in the same house same manner, several will not reduce it. Its an ideal, not a guarantee. Keeping the major detritus removed from the system and not sinked up in the bed gives the best chance of true n2 degassing, the ideal reason to keep a dsb. planting areas for roots and holdfasts are nice, extra bacterial support which winds up as suspended floc bits are part of the food chain etc