I had a straight bimax (4mm/15mm) advancement for sleep apnea and my occlusal plane was/is naturally flat.
Problems with straight LeFort 1 advancements only arise if it is a big movement (i.e. 1cm+). Your nasal base will become very full in profile and the nose very wide from the front.
In my case, my upper lip advanced 2mm and my nose got 1mm wider - if at all. My cheeks look better in profile. It was a solid improvement overall, but it's not like a live changing transformation (not that ccw would have been one either). The biggest improvement came from the 15mm BSSO anyway.