How does the use of the CSS preprocessor and postprocessor affect development?

Question

css

Hello!
I am a novice coder who wrote in pure CSS, I was faced with the fact of the existence of preprocessors and postprocessors . Their application is not entirely clear, it is only clear that they improve life in some way. So, could you briefly explain to me how they make life easier and whether it is worth using them or continuing to write in pure CSS?
To be more precise:

1. What is the difference between postprocessors and preprocessors?
   
2. Does the site load / slow down their use?
   
3. To what extent is this or that solution capable of accelerating the development of the site and does it accelerate at all?
   
4. How can you speed up development? (if it speeds up)
   
5. What is the difference between SASS and LESS? (not better/worse, but pros, cons, differences and recommendations)
   
6. does the back end affect usage? (let's say, as an option: using LESS you need to use some framework or Ruby library for it to work)
   
7. What preprocessors and postprocessors do you use and why? (I repeat: not better / worse, but pros, cons, differences and recommendations)
   

I would not refuse your personal additions on the issue.
I ask for objective reasoning, preferably supported by facts and documentation.
Many thanks in advance!

Answer 1

Generally speaking, it becomes less routine - monotonous repetitive actions.
In order not to guess - immediately select SASS in the SCSS syntax. You need a high-speed implementation of libSass, which you fasten to gulp. Then you add an autoprefixer to this, which will allow you to forget about manual prefixing. No more "post-processors" are needed. But before proceeding with this step, you must have a good knowledge of CSS.
Here is a good tutorial for beginners
https://scotch.io/tutorials/getting-started-with-sass

Answer 2

SASS works on the backend, regular CSS comes to the browser.
LESS works in the browser, so the overhead costs on the client increase both due to the additional download of the library and due to its operation.
And both approaches solve the problem approximately the same - to add to CSS something that is not there yet, in particular variables and calculations on the fly ... Well, in general, at least on Google, at least on YouTube there is simply indecently a lot of information, and you can literally do it in a couple of days dabble in theory.