During last night's ride, I had a short conversation with The Veteran about his bicycle and bicycles he owns and frame materials, etc.
The Veteran was riding a $600, maybe $800 Bianchi, a simple hybrid bicycle with fatter tires. He said he owned a high-end aluminum Cannondale, and a Litespeed (Titanium, top-of-the line) bicycle, as well as so many other frames he doesn't even remember how many he had. So, why was he riding a "cheap" bicycle? Without getting a straight answer out of him, I assumed it was because he worried about additional wear-and-tear on his favorite bicycle. Or maybe his cheaper bicycle was a more comfortable geometry and having wider tires was comfortable in the city. And it didn't matter to be seen with a cheap bicycle.
He claimed himself (as a veteran racer) not to be able to tell the difference between aluminum, steel, carbon fiber, or titanium frames. And said it largely did not matter. He said that the editors of Bicycle Magazine themselves could not tell the difference, assuming they were the same tube size and painted black. But it matters to some people, especially those bicycle companies who are trying to sell more expensive frames.
What are the differences in weight? The weight for the lightest steel frame is about 1 pounds, compared to a carbon or titanium frame. Your average high-end road bicycle weighs about 20 pounds, so that's a difference of 5%.
There are other practical reasons, such as durability (steel rusts, though does not easily fatigue), and aerodynamics to chose one material over another.
The local bicycle owner, Larry at Perfect Wheels, does not own a scale, and says he doesn't care anymore about measuring grams. But I do know that he builds wheels based on rider weight, he will not overbuild anything to add useless weight.