Who it's for, and when
It's a simple position: the basic version needs nothing more than a sturdy chair, and no particular flexibility. It'll appeal to the woman who likes to take the lead, since she sets the rhythm, the range and the depth. And to the man who likes to sit back, watch and caress.
As for body shape, long legs give the hips more range of movement. With shorter legs, or when your feet barely touch the floor, rely on rocking the pelvis back and forth.
As for timing, it's the position for urgent desires, when you have neither the time nor the room to lie down. You can stay dressed (a hitched-up skirt is enough), and there's a chair in almost every room of the house.
Precautions: check that the chair is stable before the two of you get on it. If penetration hurts, stay slightly raised on your feet, and if the pain persists, talk to a doctor or a sex therapist. If you're pregnant, have painful knees or a bad back, or limited mobility, ask a health professional for advice first.