The pluses for eye contact that I can see are:
1) Getting NT teachers and annoying relatives off your case.

2) It is hard to learn about facial expressions, and related conversational context while not looking at a person's face.
2a) It probably helps exercises the brain to interpret sub-contextual information and it may help the brain develop the means to do so.
3) I think it keeps his mind from drifting off, at least a little, in the middle of conversations, when he looks at people.
Reasons not to push it (as far as I can tell):
1) It can be damn uncomfortable, because people transmit too much overwhelming information through their faces.
2) Emotions may be processed in different parts of the brain than other visual stimuli, and while the practice is probably useful, people assume the person is paying attention/absorbing information that they aren't.
3) Sometimes it is easier to concentrate on the auditory messaging (especially if you have auditory processing issues) without the visual stimuli draining attention and effort.
3a)Sometimes I honestly "hear" and retain more information with my eyes shut and when people assume I am drifting off, then when I am looking at them and they think I am understanding everything.