Not to cause explosions, but to make very difficult reactions happen. They help very large molecules combine. Something else interesting about catalysts, if you look at the graph, you will also notice that when the activation energy is lower, the products can combine easier also. So the forward and reverse reactions are both accelerated. There is something called an inhibitor which works exactly the opposite to catalysts.
Inhibitors slow the rate of reaction, sometimes even stopping the reaction completely.
You might be asking why would anyone need those. You could use an inhibitor to make the reaction slower and more controllable. Let us introduce Lisa Meitner. She was an Austrian chemist who worked with a guy named Otto Hahn. She has the head of her physics department in Europe until she had to leave during World War 2.