High-efficiency laundry detergent should always be used in high-efficiency, also known as HE, washing machines. Standard detergent should never be used in an HE machine.
Standard laundry detergent produces high amounts of suds, which can damage the internal parts of an HE washing machine. In addition to causing damage to the machine, the extra suds from regular detergent are difficult to rinse away in an HE machine, and the excess soap damages the clothes as well. Overusing HE detergent can cause the same damage as using standard detergent, so always use the recommended amount, even for heavily soiled loads. Even though it produces less suds, HE detergent cleans as well as standard detergent.