i THINK this becomes more apparent when there is vertical movement done on the chin. I base this on all the before and after results I've seen on all kinds of SG's. I don't know the exact science behind this, only the experienced surgeons who know what they're doing know. I will say that it's usually one of those negatives that you're gonna get despite the positives.
Although some people have a lower lip that hangs too low naturally for their liking, then it can actually be ideal. I was one of those, so I was pleasantly surprised when I had a slight 'lower lip lift'.
I'd also like to add that I have seen people say that SG's have actually caused the reverse for them(lower lip somehow having less support afterwards). So again, this seems like a very complicated unpredictable issue.