They were marketed as sleeping pills. The problem was that, once they took effect, who would want to waste that feeling on sleep?
I first took them around '72-'73 in High School when they were still a new-ish drug. A friend was selling them at 3 for a dollar so, assuming that they would be similar to reds (same price, same strength, right?), I took 2 at lunchtime then went to my drafting class. When they came on I couldn't stay on the stool... just kind of kept melting off of it. Luckily I sat at the back of the room and when the teacher's back was turned managed to sneak out and walk home.
I always thought it was funny that, when you took ludes, you could be walking through a door and suddenly have the wall next to it jump out in front of you and bash you in the face. Damnedest thing, that.