The value of a non-peer reviewed article is debatable and entirely down to each person's opinion. They are sometimes favored because they are not normally directly connected to the writer or author of the article which means it is in essence the direct view of the author. They are often helpful if you are specializing in a topic and want to know if an article or paper is any good before reading it. The reason it is helpful is because a non-peer reviewed article is an article that has been reviewed by someone who is an expert or professional in the particular area, without necessarily being a part of the research or even working for the same company.
A peer reviewed article is still an article that has been reviewed by an expert in the field or topic of study, but it is usually by someone closely linked to the author. For example; if a student were to write an article then it may be distributed to other students and one of these may write a review on the article, or perhaps even the teacher. This means that the reviews can sometimes be biased and not as accurate as someone who is still an expert but may not know the author as well or even at all. Thus a non-peer reviewed article can be seen as more valuable when weighed up against a peer reviewed article.
A peer reviewed article is still an article that has been reviewed by an expert in the field or topic of study, but it is usually by someone closely linked to the author. For example; if a student were to write an article then it may be distributed to other students and one of these may write a review on the article, or perhaps even the teacher. This means that the reviews can sometimes be biased and not as accurate as someone who is still an expert but may not know the author as well or even at all. Thus a non-peer reviewed article can be seen as more valuable when weighed up against a peer reviewed article.