Receptors are a very important protein target for drugs, allowing control of signalling pathways. This is important, allowing cellular processes to be controlled clinically to help treat a condition or disease.
It is beneficial to artificially control receptors, as controlling biological processes is of great importance. For example, pain relieving drugs (analgesics) such as paracetamol, reduce the sensation of pain and are therefore desirable to administer.
Agonists cause activation of receptors, while antagonists prevent the receptor from being excited.