Something that's really really really useful. You don't know how your grandparents survived before it came along. When yours blows up over the weekend you grudgingly fork-out for the afterhours call out fee because you can't face another day without it.
This planet is a usefulnessity. I would die without it - or float around in space until I died.
When you are fucking a girl and you spin her around on your cock so that she's in a different position or if you're good enough You can land her in the same position.
Also possible with anal sex. Straight and gay.
So I was fucking this chick doggy style last night and I did The Windmill so that she was on her back so that I could see her tits.