Vinegar used in bread making reacts with the yeast or baking soda/bicarbonate of soda creating carbon dioxide gas/bubbles which really help the dough to rise. You can make it without the vinegar but the difference in how the bread rises WITH the vinegar is dramatic! Try with and without and you'll really notice the difference. The small amounts of vinegar used are not even noticeable tastewise in bread/baked goods.
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Some sodas/powders are more heat sensitive than others - there is a whole science behind them, which is used by food manufacturers to minimize production time.
If the bake time is short and the mixture is at room temperature to start with, optimum rise might not be achieved.