Baking - Chicago,IL

yeast takes longer (2-3 hours) while baking powder will rise quicker. When baking with yeast you need to let dough sit to rise while baking powder does not. They are not interchangable though, if you subsitute one for the other you need to tweak recipe (cant just substitue) I awlays bake w baking powder and baking soda.

ADD -this explains it well

Recipes utilizing yeast usually must be allowed to "rise" before baking. This is because yeast is a microorganism that converts starch into alcohol and carbon dioxide. As the yeast cells slowly begin to act on the starch, bubbles of carbon dioxide are produced which are then trapped in pockets within the dough, creating the "rising" action.
Yeast is most effective when the dough contains a high amount of gluten, a starchy, elastic substance found in wheat. Gluten helps to keep the carbon dioxide bubbles contained inside the dough, thus aiding in the rising process. When heated, the carbon dioxide expands further, which makes the dough rise even more.

Baking soda and powder rely on chemical reactions for their rising power. When baking soda and powder are mixed into a recipe, they react with acid and heat to vigorously produce gases. This is why you will often see lemon juice or buttermilk (high in acid) added to dishes that These gases expand rapidly during the cooking process to create the "rising" action.
Since this chemical reaction takes place during the cooking process and does not depend on the elastic properties of gluten, it is successfully used in situations where yeast is not suitable.

Are you asking about substitutes or yeast vs. "quick" breads? I personally LOVE yeast breads but don't always have the time to make them. I've never tried substituting. We do make real pizza dough every week or every other week and use regular yeast in it (pizza yeast never seems to work right).

You've gotten some good responses so far on this. My only simple explanation is that yeast and baking powder/soda are all different animals. Baking powder and soda rely on a chemical reaction to make things rise while baking. Yeast is a natural thing that relies on, essentially, some fermentation to make whatever you're making rise. They are not really interchangeable in recipes since for yeast breads you need warmth & a little sugar (or honey) to activate the yeast. Baking powder/soda work best with something with a little acidity to make whatever you're making nice & fluffly (think buttermilk pancakes being fluffy). If you left bread dough out with baking soda used as leavening, it might initially rise a little, but then fall (like soda pop going flat when left out).

Recipes are specially formulates for one leavening agent or the other. Baking relies on exact measurements and ingredient combinations to make the item come out properly.

Taste, rise, size of loaf, texture. Everything really. Yeast also allows for you to freeze and bake later. Baking soda and powder are use once and bake now. This is because yeast is alive and it sleeps while frozen then comes back when thawed. Soda and powder are chemical reactions with liquids in the baked good.

I think it all depends on what you are making and how much time you have to spend on it. Cakes I use powder and soda. Breads like cinnamon rolls and such, I use yeast.