The entire point of Github is "social coding".
Personally, I fork repositories when:
- I want to make a change.
- I think the project is interesting and may want to use it in the future, but have no easier way of saving it for later on the device I'm currently using.
- I want to use some or all of the code in that repository as a starting point for my own project.
Now I've heard of people collecting stamps and seashells, but why would anybody want to collect repositories?
There's nothing (that I can think of) that can go wrong from forking repositories for personal pleasure. Honestly, I keep a folder of interesting projects that I see on Github and other places simply for inspirational purposes, and partly because I'm a geek. I understand that I don't have to fork the project to read the code, but I may actually want to edit that in the future.
Now start forking.