If you guys are talking about the vibrato that is done with altered speed for effect here and there, I was told once that it's an American invention. Previously, people used to use the "goat like" continuous vibrato for just about every kind of music. The non-continuous effect-style vibrato is just that, an effect, like false fingerings or slap tonguing or something, and likewise, not using it is an effect. For flavor. And the way it's done is often different from player to player, so it's very individual. All that adds depth to whatever you're doing, but particularly in an improvisational context.