Why adding SQL Server user to "Perform volume maintenance tasks" improves database resizing so much?

If I want to create 5GB database with

CREATE DATABASE [test]
 CONTAINMENT = NONE
 ON  PRIMARY 
( NAME = N'test', FILENAME = N'E:\2012\test.mdf' , SIZE = 5529600KB , FILEGROWTH = 1024KB )
 LOG ON 
( NAME = N'test_log', FILENAME = N'E:\2012\test_log.ldf' , SIZE = 1024KB , FILEGROWTH = 10%)

it takes 1 minute on my SSD.

But when I add SQL Server user to Perform volume maintenance tasks

it takes only 1-2 seconds.

Why is that? Can someone explain to me what are the reasons for this?