What is the purpose of 1 click installation of Drupal on Web hosting?

I am in process of making first Drupal 7 website and for that searching for the web hosting. And I found that, several hosting says 1-click Drupal installation. But as I was searching the net for standard practice of site development, many sources explains Develop the site on local environment and then transfer to the web server (which includes, transfer of database, and whole drupal with modules) which is quite convincing that you develop locally and transfer to web so it start working there as it was working on locally.

On the other hand, what is the use of 1 click drupal installation on web server, I believe it will install the fresh core drupal, so from again initially I have to start developing, installing each module so, starting from square 1.

1. So, which is the BEST practice for making web site live, shall i develop locally first or develop directly on web server?

2. Simultaneously, what is the best practice about maintaining site, I read that, there should be One live site where visitor will come, Second Test site which is similar to live, One local site, So what is the standard practice for this, and how to maintain?

Very thanks in advance.