Jade, what is this for?

Question

Preprocessors

What is a preprocessor for?
Not only Jade but also Sass , Less , and others Isn't Emmet up to the task ?
But after all, in order to use these buns, you need to install so much, superfluous, unnecessary. It’s still not enough to install, but even if something happens and compilation, isn’t it more convenient than poke your finger on three keys

Answer 1

Understand already that emmet and jade/sass solve different problems.
Emmet expands short abbreviations into full expressions at the time of coding, which gives a significant speed-up in work. But that's all he can do.
Preprocessors and templating engines process your code after it has been saved. They allow you to neatly structure the code, dividing it into logically complete blocks.
The template engine allows you not to copy-paste a bunch of product cards in the catalog (for example), but to write a cycle and use a single card sub-template in it. If necessary (and during layout it is usually required), then we change the card code only in one place, and not a dozen or two accumulated ones. These are just a couple of examples of using the template engine, but they also show that you can’t drag Emmet here.
Preprocessors also provide a bunch of goodies and features: variables, mixins, conditionals and loops, and a lot of things (emmet is also not in business here). To be honest, all this has been chewed up many times on the Internet. You should read a few articles on the topic, not ask questions.