Downloading and unpacking Drupal core and the desired contrib modules using drush download or drush make is only the first step in building a Drupal site.  Next the database must be created, populated with data, and the initial configuration applied. Once again we have two choices, Drupal's built-in install.php or Drush's site-install.

install.php

• prompts user for information about the site and the site administrator
• allows user to chose from a list of profiles
• install.php cannot create the site database and dbuser
• settings.php must exist and be writable during install and manually changed to read-only after
• webserver must have write access to sites/default/files

drush site-install

• information about site, profile, and site administrator input via command-line
• can create the site database and dbuser, if supplied the MySQL root password
• creates settings.php from information supplied on command-line
• leaves settings.php world readable
• creates sites/default/files owned by the uid running drush, usually root