In which case, clone() and fork is better than pthread()?
===

I am beginner in this area.
I have studied fork(), vfork(), clone() and pthread().
I have noticed that pthread_create() will create thread which is less over-head then creating a new process like fork() and thread will share file descriptors, memory, etc with parent process.

But in which case fork() and clone is better than pthread. Can you please explain me by giving real world example.
Thanks in Advance.