Some users on Wefunder might be more qualified to perform due diligence in certain businesses that match up with their skills and experience.
While you should never outsource your due diligence, you can use the judgment of the co-investor you are following as one factor in your investment decision.
When you co-invest, you might help the investor you are co-investing with have more power and leverage to ask hard questions. For instance, it is unlikely that a founder would spend an hour talking to an investor who only wants to invest $100. However, if that person has many co-investors who might invest a collective $50,000, it is more likely the founder will consent to an interview.