They provide dimension to a flat surface
Curiosity – where did they come from? What is their history?
Tradition – women kept a button box or jar for mending or sewing clothing
Interesting to look at
Provide a focal point, or place for the eye to pause
Connections – between women; between lays of fabric
Closure/safety – “Button up your coat because it’s cold outside”
For some unarticulated reason, I sometimes use a button to represent a face in a very abstract way.