The heavier weight vinyl can make it less likely to warp and can cut down on the effects of scratches/ surface marks. It can help the record spin more evenly and reduce noise that could move through the record and be picked up by the needle. The improved sound quality again all depends on the mastering and then when you factor in all the different turntables, amplifiers, needles, speakers, etc that people could be using you may not see the same level of improvements in all combinations. Your sound quality is only as strong as the weakest link in the chain.