Scramble porn is the kind you get when you aren't paying for actual reception. It's many a child's first introduction to filmic erotica. And MAAAAAN is it hott!
When I was wee, my parents got that nifty cable box that sat on the TV and gave us all those glorious R-rated channels - Showtime, HBO, and the Playboy Channel. So to speak. My parents didn't pay for them, so they came through scrambled. Not an obstacle for a horny youngun, though; I'd crouch by the TV, hand on the cable box in case of sudden parental appearance, and revel in the sexxxy heavy breathing, suggestive dialogue, rhythmic bodily pulsing, and occasional emergence of nudity.
Scramble porn gave me beautiful, hazy, hallucinatory, phantasmagorical erotic dreams and spawned my lifelong appreciation for Emmanuelle - before I'd ever truly seen her in action.
As an adult, I've watched a handful of unscrambled porn films, and they've always disappointed. It's only marginally exciting to see closeups of actual genitalia; I much prefer the mystery and, well, inflaming frustration of the scrambled variety.
jmpz recommended this fine article:
http://archive.salon.com/sex/feature/2000/10/25/scrambled/index.html