The main factor with gradual engagement bringing higher quality signups I would assume is with how often of exposure you can have to the future potential user -

The main factor with gradual engagement bringing higher quality signups I would assume is with how often of exposure you can have to the future potential user - in a non-intrusive way. Seeing someone using an iPhone, who then shows you something on it - or shows the phone off to you - would be an example of this.