The value is not needing to change every other syscall and not needing to write new ones with a pid argument (besides which, what when you want to change it to a pidfd argument? then you add pidfd_syscall instead of duplicating every syscall again)

I meant the value of running syscalls in another process from the parent process in contrast to (v)forking and running them in the child directly.

The value is starting the child with a clean slate instead of a copy of its parent.