Higher weight makes the underwear "wrap" around the top of the chair more securely, but too much can cause "glitches" or inaccuracies. Around 1.0 is usually fine.
Higher weight also for some reason seems to make it more likely to hide the butt, you can increase the weight of the "butt_crack"/"ass" prompts [ex: (butt_crack:1.5)] as well as add things like "lowered pants" or "bare thighs" if you want to show that part off.
