sc_url_library :- when useful?

I’m looking at one sample code with 8.1 which has this in the blank app:

<link rel=“stylesheet” type=“text/css” href="<?php echo sc_url_library(‘prj’, ‘bootstrap-3.3.2-dist’, ‘css/style1.css’); ?>"

What advantage does this offer over referencing the CSS file directly?

Because this way library goes with your project.
Prior to this, you have to copy manually.
For example, I have some js and libs I develop outside SC and use from SC, but every time I deploy, backup and so on, I must take care of this lbs backuping manually, or copying manually on deploy

oh cool, thx!