Why should I add co-authors on Google Scholar? Google Scholar wants me to add areas of interest, photo, and co-authors. I understand why I may want to add the first two, but why add co-authors? All the publications already list the actual co-authors. Is it an attempt to turn the site into more of a social network? Is it an excuse for Google to spam them ("X added you as a co-author!")? What is the benefit for the profile owner?

For example, I have some papers with dozens of authors. Should I "upgrade" them to "co-authors"? I have no idea who some of these people are, but maybe the goal is to get as many as possible. On the other hand, if I don't add someone I actually know, will they be offended?
In general, I find the Google Scholar profile pages to be elegant and useful. 

Some people choose not to add co-authors to their profile pages. You might not see any benefit. You might not want to play favourites (i.e., who is enough of a co-author to be listed; what if I forget to add someone, would they be mildly offended).

In general, random people will google you and land on your google scholar profile page. Seeing who your main co-authors are might be useful to such people to give them an understanding of where your work is situated and who you are working with. They can then also more easily explore the academic work of your co-authors.