It may be necessary to run the installation step more than once to cover the order of package installation; some packages installed early may need to have later packages installed before they will configure properly.
"Debian GNU/Linux: Guide to Installation and Usage"
John Goerzen and Ossama Othman
However, sometimes you need to change important system files; for example, you might want to install new software or configure your network connection.
"Debian GNU/Linux: Guide to Installation and Usage"
John Goerzen and Ossama Othman
You can also configure filesystems to mount automatically when the system boots.
"Debian GNU/Linux: Guide to Installation and Usage"
John Goerzen and Ossama Othman