Sure, but it's not the only reason to use them, you can improve mouth feel and prevent melting even if the fat content's higher. I'm struggling to prove a poin

Sure, but it's not the only reason to use them, you can improve mouth feel and prevent melting even if the fat content's higher. I'm struggling to prove a point because Waitrose doesn't seem to have any as high as 18% (the highest at 15-16% being own label & YeoValley, notably both using egg) – the more expensive brands like are lower fat and do have LBG/guar. Also bear in mind low-fat can be a goal itself, or vegan compatibility.