Welcome Guest! (App Version 5.16)
Sass files whose name starts with an underscore and in turn they do not automatically compile directly to CSS. In fact they are first imported to the main sass file and then this main.sass (or primary sass file of project) gets converted to CSS and thereby included in HTML Page.
The benefit reaped of this process using partials is that - the project does not require all the code to be botched up in 1 single file. Rather, the project can be split into different modules and functionalities and Sass file can be made 1 for each of them. Then all these separate Sass files can be imported to 1 main file and then this single file will be compiled to CSS.
Example of breaking up project to multiple Sass files can be done as follows:
_reset.scss _variables.scss _mixins.scss _functions.scss main.scss
Note that there should be 1 file at least which is not a partial and will include all partials within its code.