Modeling has gotten progressively easier throughout the years. We no longer have to calculate every length and angle by hand when we sketch out parts on paper, the computer does it all for us. One of the many benefits accompanied by the technological advancements made is that parts can be modified without needing to start from scratch.
For example, I was tasked with creating a part in NX, and then changing an angle to change the shape of the part. Afer construction the part, which includes sketching and constraining the 2-D sketch to make sure later modifications would go smoothly, changing the shape of the part becomes as trivial as entering different angles to alter the shape.
Both parts were created using the same sketch, the only modification was the changing of one angle between the three circles.