This is also called the Knee Trembler. It is a cool position for straight and same-sex couples and is great for quickies. Penetration might be difficult if the partners are not more or less the same height. In such a case, rather try the standard rear entry position.
If the woman is much shorter, she could rise up on her toes and turn one leg slightly sideways. The man could also aid penetration by bending his knees.
For more tips and techniques, visit Health24's Sex Zone.