This position is for those people who enjoy slow motion sex. The angle for intercourse is not conducive to vigorous thrusting. The woman sits on top of him, with her legs straddled around him. This creates a perfect opportunity to hug for a few minutes and be intimate. Sitting on top of each other and maintaining stability is a formidable task for most people.
Some people prefer facing the same direction.
This is preferable for those who feel less coordinated or embarrassed. You do not have to face the other person. Sex is funny. Great chairs include rocking chairs, kitchen table chairs and, of course, the chair in the office. Sex on a chair makes for a good study-break.