Wood is one of the biggest developments in evolutionary history, especially in respect to the development of human technology.
If you're ever in nature, you can see places where all sorts of plants are competing for their spot in the sun. Some grow higher than others, others develop larger leaves. One can imagine what an advantage it must have been for trees to evolve, using trunks made of wood they can hold more weight, elevating their leaves over all the other plants, stuck at a few feet tall. Of course this started a new race between trees to grow taller and taller.
Wood is a pretty amazing thing when you think about it. It is light weight relative to it's strength, can hold a tremendous amount of weight, especially compared to a regular plant stem, and on top of all of it's amazing structure qualities, it provides the trees with water, nutrients, and protection.
It was truly a gift to humans, giving us a material with all these wonderful qualities to build with. Buildings, furniture, weapons, and tools are the first thing that come to mind. But possibly even more importantly than those uses is that is can be used as fuel. The invention/discovery of fire is widely touted as one of the most important developments in human history. Imagine if there was no wood; people couldn't rub two sticks together to start a fire. Of course flint and steel is another method that could be used to start fire, but you can't get steel without fire.
Lets assume we could get fire through another method, perhaps lighting, without wood, fires would be made of leaves and brush, burning fast, and only a short time. Not useful for keeping animals away over night, smelting metal, cooking large pieces of meats or stews.
Not only would there be no wood to build structure, but no steel, iron, not even bronze. No mining tools could be developed. It may very well be the case that we owe all our technology to the glorious tree.