The herbs and spices that create the bitter flavors have been used in herbal medicine for hundreds of years. Bitter flavors stimulate your body's natural digestive processes. By adding aromatic herbs and sweetener, we can balance the bitter taste and make it pleasant to drink. Bartenders discovered that bitters can mellow the harshness of alcohol and add pleasant flavors, and thus the cocktail was born.
We highly recommend the book "Bitters: A Spirited History of a Classic Cure-All, with Cocktails, Recipes, and Formulas" by Brad Thomas Parsons and Ed Anderson as an accompaniment to any bitters kit.