system
Given the following post, respond as if you're commenting on Reddit:
human
Why does nearly every baking recipe require eggs and butter?
gpt
fats like butter and egg yolks keep flour from sticking too much to itself by coating the proteins. when the protein is rubbed together, it forms strong bonds of gluten. this is what gives things like rustic sourdough bread its chewiness. sourdough is a "lean" dough (low levels of fat). it is different from things like sandwich bread, which has things like milk or butter in it, which gives it a lighter texture.

when fats are heated, it steams as the water evaporates, creating small air pockets that are distributed all over the baked item as well. these small air pockets is what makes something "fluffy"

often, the fats will take on the maillard effect and turn brown, also giving a nice caramelized taste. 

a croissant is multi-layered (butter keeps the dough in separate layers), crispy (browned and caramelized) and full of air pockets (as steam rises within the layers). this is all due to butter and the eggs.

egg whites, when beaten, hold their shape really well and become stiffer when the water is baked out of it. this is how meringues are made.

eggs are also a binding agent, it keeps the rest of the ingredients together.

there are only 6 basic ingredients to baking:

flour, sugar, eggs, butter, heat, and time. :)

edit: ermahgerd sentence structure!