30 Gallon reef cube build 100% DIY

[Frogger]

Not sure what the benefits are.

We used to put egg crate at the bottom of the tank to create an airspace and have gravel on top, ie: undergravel filter, or to create an anaerobic space in the case of a plenum. But there are way better methods of filtration and nitrogen reducing methods than these. I am not sure what other uses there are. Maybe supporting your rock.

The question you may want to ask is if you want a bare bottom or coral sand or gravel. I prefer a thin layer of coral sand or gravel.