A catalog is a part of product photography and if you sell online it's really important to have professional photos on your website.
Customers make purchase decisions based on what they see, and if the product photos are pixelated and dark, they are less likely to even consider the product, regardless of how good it may actually be.
They will provide customers with the maximum amount of information possible about the product, including its quality, materials, appearance, shape, colors, and sometimes even size.