My old canopy bed had them. It was kind of cool but that frame was ridiculously impractical so it didn't make it in my last move.
I never understood why everyone thought it was a sex thing. I just found it useful to spot the cat lurking in the room, so I didn't have to sit up to check on what I thought I saw moving.
What is much more of a sex thing is a mirror in the headboard (which that bed also had lol), or near the foot of the bed, so you can make eye contact