Jeff Berlin is a big advocate. And I believe it's where the notion comes from. The intent is that you're forced to use controlled playing.
I think you have Jeff mixed up with Gary Willis who pioneered the concept and actually uses it on his bass. I've never seen Jeff with a ramp... in any case that's not where the idea came from.
If you've ever played on a bass with pickups close to the strings it's very similar to that. It extends that feel to a larger area. I think it was a brilliant idea on Gary's part... as someone who always dug that feel, I always pondered how nice it would be to have that feel farther away from the bridge or neck pickup. Just never took it to Gary's conclusion.
While you can use it as a thumb rest, it's really not about that. In fact most folks I've seen who use them don't rest their thumb because they use a floating thumb technique which greatly aids in right hand muting and comfort.
IME while it initially does make most people play with a light touch because it keeps your fingers from going too far past the strings when you pluck, I found that I pluck more parallel to the body and in fact you can actually pluck very hard once you get used to it. The forcing you to play light thing is a misconception IME IMO. You can play hard too. And if placed correctly they don't have to interfere with other techniques.
PRS has a derivative of the ramp, calling it a "manual compressor" on the Grainger basses. It's basically a ramp with scallops under each string, allowing the string to pretty much sit down in a groove in the ramp. Probably seemed like a good idea on paper but with it setup low it forces you to pluck across the top of the string because you cant get to the sides. Didn't care for that feel at all.
I have them on several basses and most folks look at it and the low height of my strings and instantly think it must be unplayable. I encourage them to go into "shut up and play" mode and most are surprised how little difficulty there actually is to it. I just sold a bass with one a few days ago, it was the first time the bassist had played with a ramp and he was apprehensive. The day after he got it he called to tell me he wanted ramps on some of his other basses.
It can happen that quickly.
