I'm not a baking guru, but I do make pancakes, pastry dough, and various confections, etc quite a bit. As I understand it, baking soda is more about the PH level than it is about a rising/leavening agent, but PH level also affects rising. Baking soda is alkalinem lowers OPH level, and increases browning (Maillard reaction), hence increaing flavor.
FWIW, I use both baking powder and baking soda in my pancakes, and I usually add a little lemon juice and lemon zest to the batter (acidic). I general rule of thumb I use is 1 tsp baking powder and 1/4-1/2 tsp baking soda per 1 cup of dry ingredients.
Everything we cook with has a PH level, and most things are acidic. Most seasonings are acidic - salt, sugar, honey, vinegar, etc. Baking soa can also be used in dry spice rubs to enhance browning.
The baking soda and the baking powder in cobbler biscuits provide leavening. But did you know that the baking soda also serves another function? It enhances browning. In fact, many pastry chefs add a little baking soda to baked goods to promote browning, rather than to cause lift and rise.
Browning, known as the Maillard reaction, is an extremely important phenomenon in cooking because browned food tastes better. When carbohydrates and proteins are heated together the sugar (from the carbohydrates) and the amino acids (from the proteins) combine to form hundreds of new, distinct flavor compounds. This means that browned food has much more complex, interesting flavors than food that is not browned. So anything that increases browning is a good thing.
Why does baking soda increase browning? Because browning occurs best in an alkaline environment. Here's how it works. An amino acid molecule has two ends--one is the amino end and one is the acid end. As you might guess, the acid end is acidic, but (as you might not guess) the amino end is alkaline. It's the alkaline end that has to react with the sugar molecules for browning to occur. In an acidic solution, the alkaline ends are destroyed. In an alkaline environment, the amino ends thrive and they can react with the sugar to create browning.
The biscuit portion of our cobbler recipe contains buttermilk, which is very acidic. Baking soda, being an alkaline itself, reacts with the buttermilk to create a rise in the dough, but it also creates an alkaline environment, thus permitting the amino ends of the amino acid molecules to react with the sugar and produce browning.
A biscuit recipe with buttermilk and just baking powder may or may not rise (depending on how much you use), but it certainly won't brown very well.