Red hair has become a popular trend. While most red-hair follows the "scene" style, not every girl dyes it for that purpose. I too have dyed my hair red, and never will I do it again. Through observation, I have come to these conclusions on why girls dye their hair red.
1. They are an introverted person wanting that boost of attention to help them be bold.
2. They are one of those girls that constantly change their hair color and like to change and experiment.
In both cases I noticed something else... Girls will either stumble upon or search for a photo of a girl with red hair. When they see a photo of a pretty girl who is rockin the red hair, they feel the need to imitate their hair in hopes that they will feel as pretty as they view the girl(s) in the photo(s).
Pros: Dying your hair red is something good in my opinion. It shows that you're bold and helps you become less insecure, plus it's always fun to try something new.
Cons: most shades of red are unnatural looking and can cause a lot of negative perception from society. Red fades fast, is hard to maintain, and difficult to remove.