Question on IHA

I had a question on IHA when ordering shades, specifically Triathlon Roller Ess. I understand that all the shades have "regular" IHA based on matching widths and heights, ensuring identical hembar travel.

My question lies on when to select the IHA option in SCT - for example, it makes sense to include this when you have large variations of shades sizes in the same area, but what about where you've got about 1/4" of difference in height and width on a few shades? I'm not seeing an actual cost difference when selecting the option, so also curious on why not always select this option?

Thanks in advance!