Why fork() before setsid()

Question

Why fork() before setsid() to daemonize a process?

Basically, if I want to detach a process from its controlling terminal and make it a process

Answer 1

It is required to fork() and have the child call setsid() to ensure that the process calling setsid() isn't already a process group leader (setsid() wants to make the calling process the process group leader of a new process group, so it fails in that case).