If there is only one author, then it is possible to present new and exciting ideas. But with several authors, the final cut has to appeal to everyone and can sometimes be a bit boring even though it might be more correct!
Its not about good or bad for one or multiple authors, it’s about the contribution they give for a paper. For a research paper usually a number of researchers involve so usually credited for co author. But authorship should/must be given according to contribution not because their relationship with some person without contribution. I have seen different trend of authorship in different countries.
Research publication is based upon trust between subjects, authors, editors and the readers. We have to trust each other and use the results of research. If we start reading papers thinking authorships are incorrect or data is incorrect we landup getting nothing. However if we analyze the cause of all this problem, it all rests on education of our authors. ICJME has laid down strict criterion to be author. Let us follow that and let us educate others also to follow them. please read the following link. http://www.icmje.org/recommendations/browse/roles-and-responsibilities/defining-the-role-of-authors-and-contributors.html