Because it is a fashion. When this fashion is over, what will you use social networks for?
Like everything, social networks will be replaced by something else. The importat thing is to use this fashion to be useful for you, without exagerating.
Use networks for:
- Keep your circle of friends growing.
- To be informed about what your friends are doing, the next time you will meet them personally, there will be more stuff to talk about.
- Give your opinion about lots of subjects.
- Expose your new ideas and ask for feedback
What else do you use social networks for?