I've read more than once that the closest eye to the camera should be focused on a portrait of a person or of a group of people.
Here is an example (faces are blured for discretion, pay attention to the unblurred eyes). Although all faces should be in focus, some of them are a little shapier than other ones.
But why not focus on the person who is not the closest one to the lens neither the farest one, so on average, all faces in the picture will be more focused than the first approach?
The least sharp face on the second approach will be sharpier than the least sharp face on the first approach, right?
In the example picture, it would mean changing the focus from the right eye of the closest guy to the lens to, maybe, the guy in blue.
Even if sharpness is not evenly distributed (there's more depth of field behind the focus than in front of it), as it is said in this related question, even though it seems reasonable to focus maybe on the second face closest to the lens.