It is commonly used when heavy rock formations are used in the aquarium,preventing pressure points from occurring along the bottom of the tank..assuming you'd be using sand in the setup as Africans love sifting/digging in the substrate causing rockworck to settleh&possibly cause damage...cut the egg crate to size,place in bottom of tank before adding substrate,build rockwock on the eggcrate so as it has no room to settle&fill in around your rockwork(assuming you'll be using some form of rock)...I had almost 100lbs of lace rock in my 75g African tank with no issues...