Drupal version control - professional development
If you've got a complex setup, you may want to look into the Aegir project, which is a Drupal-based tool for managing Drupal site installations.

If your needs aren't big enough to require Aegir, a lot of the tasks which it does can also be automated using Drush, which is a command-line tool for managing a Drupal site.

Even if you feel Aegir is overkill, you should definitely use Drush - it will make your life a lot easier when it comes to deployment between your development and live versions and management thereafter.

As for version control: If you're writing any of your own code, then yes, you should be using version control. If you're simply using Drupal plus third-party modules, then you probably don't need it, since you're not in charge of the code anyway. But you might find it useful nonetheless, because there's always a chance you might find yourself needing to tweak a third party module (or even the core) to get things to work the way you need to, and at that point you will need version control, and it will help if you already have it set up.

You can't very easily do version control on your site content, because it's all in the Drupal database. You can do a certain amount by moving your site structure from database to code using the Features module, at which point it becomes possible to version control it in the same way as other code, but your actual content remains in the database.

To do version control on content, the main option you have is the Diff module, which allows the database to store multiple versions of page content, which can then be administered.

Hope that helps.