An advantage is that it guarantees to wake up only threads that will not be immediately put to sleep, but a seemingly paradoxical disadvantage is that many of these threads will indeed end up being put back to sleep with expensive context switches since only one may enter the critical section at a time.

An advantage is that it guarantees the right thread will be woken up, but a disadvantage is that too many threads might be woken up that could have been left sleeping. This results in more context switches to simply put them all back to sleep, which is expensive.

A disadvantage is that it does not guarantee the right thread will be woken up, but only one thread will be woken up at a time which avoids extra expensive context switches.

The function is better in every way, there is no disadvantage.