It's useful for making shorter hardscape appear taller. Occasionally for building slopes. But it doesn't serve much of a necessary purpose.
I've used it in the past to zip tie to hardscape pieces to hold things in place but never to redistribute weight, as some appear to think is helpful. (It's not.) There are some popular YouTube videos of people piling in several hundred pounds (maybe thousands?) of rock in various tanks to show their strength.
Thanks everyone, I probably won't use it unless I find some cheap and close.
I wasn't so much thinking about weight distribution as preventing a rock from directly striking the glass if I drop one. Once substrate is in place that shouldn't be an issue I would think. So I'll just be carefully when doing initial rock placement.
It used to be and sometimes still is suggested to use egg crate or correctly named drop ceiling grid to spread the weight of rocks in a tank but it really hasn't been proven to actually work. I had it in a couple large tanks with lots of rock and it just accumulates debris and my cichlids tended to uncover it daily.
You could always use a towel or piece of Styrofoam to protect the bottom while you are placing your rocks in the tank. I've used this method before for large rocks and I always put the rocks directly on the glass bottom and then add the substrate but that is because I don't want cichlids excavating under the rock pile and potentially toppling the rocks.
Check Home depot or lowes for damaged sections if you really want to use it. Normally comes in 2 foot x 4 foot sheets.