The yeast in this pizza base really helps to make the dough a little bouncier and chewier. Without it, you will end up with a very thin and crispy base.
When using yeast you need to make sure that if you are using it from a packet that was previously opened, that it's not been open for more than 3-4 months, otherwise it's likely not active anymore.
You also don't necessarily need to add the sugar when mixing the yeast with the water either. While, contrary to popular belief, sugar doesn't help to activate the yeast, it will make the yeast froth up in the water. This is a useful indicator that you are using active yeast as it won't happen with yeast which is past it's best, so it's a helpful step to make sure that you're using good yeast.