Extra ingredients in starters
I've been thinking a lot about certain starters (like a supposedly Amish recipe that I have that includes dairy, sugar, nutmeg, cinnamon, and eggs) that have extra ingredients in them. Certain spices might permeate the liquid more, like how the flavor of soup might be enhanced from slow cooking, but my understanding is that they might also interfere with the process, as certain spices or flavorings may have antibacterial properties. I know I heard that many people have successfully put eggs and dairy in their starters, and if my friendship bread recipe is valid than obviously it has withstood the test of time and therefore it works. But is it a waste to add these extras or does it change the process in a beneficial way?
Like, if we add dairy, does that mean that we have a sourdough culture overlapping a yogurt culture, therefore enhancing the process? If we add sugar to the starter, does that mean the sugar would be consumed and the flour would not be as consumed, altering the flavor in a beneficial way, or does it mean we've just had our yeast eat the sugar and it's gone and wasted? If we use a regular starter and add these extra ingredients to the final dough instead, how is the flavor profile and yeast activity changed? Is there any benefit to having eggs in the starter rather than the final dough, does the cinnamon slow down the yeast's consumption of the final product and therefore it doesn't get the "sour" flavor profile, ending in a sweeter bread, or does the cinnamon in the starter mean your starter has a greater likelihood of failure and less rise?
I know that's a lot of questions, and I haven't gone over all of the ingredients, but... in general, what is your thoughts or experiences with any ingredients other than flour and water in a starter? Have you noticed anything that indicates something should or should not be included in the starter versus the final dough?