Rock doesn't use fuel and glass is waste of time. If I had to make things from sand, I wouldn't make it to magma in another five years, because I'd need to plant trees for fuel, and all that fuel industry, which takes much more time than some hauling.
Oh, right. I forget not everyone sets up magma industries within a fortnight from embark.
Gotta agree with Psieye, when you go for magma metal industry, you get glassmaking for free, plus it's magma-safe and infinite, so you save having to use steel tubes.
Also, clay is an unlimited building supply and no magma or processing needed. Think of the time savings on mining/hauling rock from deep underground when building above-ground structures, and it's all one colour.
I think you're talking about some exploit. I have no sand on my map, and need to buy sand from caravans. How do you get sand for free? Rocks are for free. I have clay and kaolinite (which is the best, but it is rock anyway) but it seems makers choose material randomly. And I need to glaze it - with ash. Which is also random, they can glaze perfectly good pots, already safe for fluids.
Anyway, I make rock doors, blocks for bridges, cabinets, floodgates, hatches and some other furniture (I don't need many tables and similar). And of course hundreds of mechanisms and large pots. Material is for free and next to their workshop, thanks to quantum stockpile. I use only rocks which were dig out and hauled because they were obstacles. I don't mine for rocks specifically as a material. I can't see how glass can compete. And rocks have different colors, which is nice. When I have magma I make things from nickel and iron/steel (or other fancy metal, I have never found gold so steel is the best so far). Why to play with sand when you can use metals, I don't understand. But I understand that anyone can have his or her sentiments.