This combination is used to create a pin dot pattern, which is a kind of sculptured carpet. This style is made from either a high cut and low loop pile, or a level loop and level cut pile. This kind of carpet is generally made of two colors of yarn.
Cutting all the loops at the top creates "cut pile" carpeting. According to Carpet Buyer's Handbook, this is the most popular style of carpeting. There are several subcategories of cut pile, each with a characteristic appearance: frieze, Saxony, plush and textured. Shag carpeting, popular in the '70s, is a type of cut pile.
Uncut loops create loop pile. Until Berber, a loop pile carpet, caught on with decorators, uncut loop carpeting was seldom used in homes even though it is very durable.