Question- egg crates in the bottom of the tank

Distributes the weight of the rock throughout the egg crate and not on any one pressure point amongst the bottom glass. Also - provides 'cushion' or weight distribution should the rock feature fall.

 

There are pros and cons of having or not having egg crate in your tank. Since the pros have been listed I will go with the cons. Some people believe it will cause Hydrogen Sulfide buildup in the pockets created by the egg crate. The pockets will not allow all the critters in your tank access to get in there, clean it and move it around. It can also inhibit wrasse from burying themselves to sleep unless you have enough sand on top.

 

I've cut a piece of plexiglass to fit the bottom of my 75 so the rockwork will be in direct contact with that instead of the glass. Some people also use Starboard or similar polymers if going with a barebottom tank. It also might be better at distributing weight than the plexiglass even if you're not going barebottom. Also I think both of these would be better than eggcrate because of what was mentioned, they won't create pockets like it will.