The thickness of running socks can play three roles

Makes every step softer while running. This is very understandable, the thicker the socks, the greater the cushioning effect, which can reduce the pressure on the feet and knees. It's a lot like what the midsole of a running shoe does.

Reduce the appearance of blisters. Some running socks will be thickened on the forefoot or heel and other places prone to blisters to reduce the appearance of blisters.

Fills the extra space inside the shoe. The ideal state of a pair of running shoes is to "stick" tightly to your feet, which is what we commonly call heels. Therefore, we generally choose the most suitable size and tie the shoelaces before running to maximize the effect of running shoes.

But sometimes running shoes are not as good as people want, for example, they will be slightly loose in some places. At this time, a pair of thicker socks can fill the extra space and help your feet be better fixed in the shoes.