when to use syscall function instead of c lib wrapper

Question

I was looking at the libevent code, and saw some code like this:

 int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event) {
        return (syscall(__NR_epoll_ctl, epfd, op, fd, event));
 }

What are the reasons to use it? Why would this be better than a direct call to the function?

 int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);