Well, on mobile it can be hard to quantify and connect design to value. On the web it's a different story. There's nothing wrong with beautiful design as long

Well, on mobile it can be hard to quantify and connect design to value. On the web it's a different story. There's nothing wrong with beautiful design as long as you are willing to accept the fact that at one point it is serving art and not business needs. And that's OK. If the requirement is to strictly serve business needs, then you have to A/B test, generate numbers and go with what optimizes conversions or whatever you are after. People react to what they see in amazingly different ways. I don't think anyone has a canonical "manual" for what will please most people or what will compel most people to take a given action. I mean, look at Craigslist!