Indeed, Wikipedia says the coccyx is far from useless in humans:

it is an important attachment for various muscles, tendons and ligaments—which makes it necessary for physicians and patients to pay special attention to these attachments when considering surgical removal of the coccyx.[2] Additionally, it is also a part of the weight-bearing tripod structure which acts as a support for a sitting person. When a person sits leaning forward, the ischial tuberosities and inferior rami of the ischium take most of the weight, but as the sitting person leans backward, more weight is transferred to the coccyx.[2]