They make hard or unfamiliar concepts easier to understand.
Explanation:
They connect the hard concept to something more familiar. It also allows you to add in great detail.
1 = a leaning or prejudice toward or against someone or something
5 = an indirect, unjustifiable suggestion
2 = a concise, "easy" answer to a complex problem
3 = the presentation of only one or two solutions or ideas as the "complete picture"
4 = an appeal made solely to a person's feelings