Users rely on it even more than the content of individual reviews to provide the overall picture of how other users experience a product. Without a ratings distribution summary at the top of the review section, shoppers are likely to let the first few reviews determine how positively or negatively they perceive the product, and wonder if some of the reviews are fake.
If your shoppers are rating products on some attributes in addition to giving an overall rating (e.g. fit, width, etc.), then it’s a good idea to include a summary of those attributes in the ratings distribution summary section.