Understanding parallel structure of sentences, lists, or headings helps create clear, concise, reader-focused messages. An excellent post on this topic appears in Daily Writing Tips, a useful website for writers whether they are composing short stories, essays, business proposals, technical reports, or scientific papers. There the seven examples of problematic parallels reveal how many ways we can lose focus of our ideas.
Here is an eighth example:
Non-parallel: Our organization provides help for the homeless, housing, meals, and innovative career counseling services.
Problem: Of the four provisions, only housing and meals are parallel, or conceptually consistent. The first, help for the homeless, is actually an umbrella term for the other three, so it does not belong in the list. As for the last provision, the modifiers suggest that the housing and meals fall short in quality of the career counseling, which is innovative. Solution:
Parallel: Our organization provides innovative services to the homeless through housing, meals, and career counseling.