What is the reason for minifying all css and js files?

Question

css

After installing gulp, in any folder on the computer, when editing and then saving, a copy of the file with the .min extension appears in the same folder, although I didn’t write anything for js in gulp, what could be? Css concat installed globally, but if you remove it from gulpfile Nothing is solved.
Even gulpfile.js itself is copied with .min extension after saving