Without this kind of lactobacilli, you cannot make San Francisco sourdough bread. It includes wild yeast, commercial yeast, beaten egg whites, baking powder, baking soda, and other less well known chemical leaveners. By allowing the dough and the gluten to relax for a few minutes, it becomes easier to knead the bread, and the risk of tearing the gluten is reduced. The sponge allows for increased fermentation, meaning better flavor and better rising - up to a point. Too long a sponge will create bread that's so sour that it tastes bad, and won't rise properly.
Some starters also contain potatoes, milk, yogurt, fruit, and many other things.
I personally haven't tried to use those, but I've heard that they don't work to leaven bread on their own. I have successfully used a starter whose only ingredient was applesauce, but on the other hand, I used all the starter that I made in the bread. I don't know if it would continue to work if it were kept going. Making what you need each time does seem to work. It's necessary, or at least highly advisable, for water to be at this temperature when baking bread with commercial yeast.