It isn't only for web developers. It can be useful for anyone. When viewing a web page, you can delete or otherwise change stuff, you can execute calculations,

It isn't only for web developers. It can be useful for anyone. When viewing a web page, you can delete or otherwise change stuff, you can execute calculations, you can check for various stuff, and more. It is very useful on a lot of modern web pages; they tend to be rather unusable without it.