Virtualization is a nice way to achieve a variety of goals. Try new distros. Run a virtual OS for tasks you do not want to do with your main system like install experimental programs. It is also nice to have a virtualized windows running on your system. Though I have to say during the last couple of years I rarely have needed it except for evaluating purposes. You might want to go so far as to set up a virtual server either to actually use it or for testing purposes. For this it might be nice to have a perfectly configured Debian purring in your vbox.

I wouldn't say Virtualbox is the best or perfect solution for virtualization. It is very easy to install though on both Linux and windows and delivers good performance. Virtualbox is furthermore completely free to use.

A small downside is you have to install the Virtualbox guest additions. (Besides - another advantage of Virtualbox is that many Linux distributions come with the guest additions already installed!)
Here's how to enable the Virtualbox guest additions in your Debian guest and create a shared folder you can access as a normal user to share files between your host and your guest system:

You have to login as root or use sudo before every command. (In Crunchbang and other Linux distros which have no root admin account set up you can create it by typing: sudo passwd root)

Update your system with:
apt-get update

Upgrade your system:
apt-get dist-upgrade

Install packages to enable compilation:
apt-get install build-essential module-assistant

Download and install kernel headers:
m-a prepare

Click on install Guest Additions:

debian crunchbang virtualbox

Either the file manager pops up with the CD-drive opened or you have to navigate to it - graphical or within a terminal:

thunar opens cd-drive

I was lacy and just opened a terminal from within Thunar file manager:

open terminal from within thuar

Type in:
(To have all files in the CD-drive listed.)

Login as root.

sh VBoxLinuxAdditions.run

The installation process should then start. Don't be worried about 'The headers for the current running kernel were not found. If the following module compilation fails then this could be the reason.' It always says that and always succeeds.

sh VBoxLinuxAdditions.run

Now we want to create a folder we can access in our virtual installation (guest) and on our normal OS (host).

First we create a folder in our host system. E.g. in our home directory. Lets say we call it share_host. (Mine is called _Linux_)

Next we have to shut down our virtual installation (guest) to change some settings in Virtualbox Manager.
Click on Shared Folders. Then on the green plus and add your folder:

(Auto-mount has only worked for windows guests for me.)

Boot up your Debian guest and open a terminal.

Type in: makedir /home/<username>/share_guest
You are free to choose the destination and the name of your shared folders.

Mount the shared folder and permit your normal user full rights:
sudo mount -t vboxsf -o uid=1000,gid=1000 share_host ~/share_guest
(Check whether your user and user-group has the id 1000! Just type in a terminal: id)

To mount the shared folder right from the start you add an entry to /etc/rc.local:
mount -t vboxsf -o uid=1000,gid=1000 share_host /home/<username>/share_guest
('~' doesn't work here!)



Virtualization alternatives:

Nice introductions to those alternatives have been compiled by Dedoimedo.