The docs say that it "Saves a file upload to a new location." Let's see what it really does...

Reads in from global arrays
// Make sure there's an upload to process.
if (empty($_FILES['files']['name'][$source])) {
return NULL;
}
Accesses global variables
global $user;
Validates input
if (isset($validators['file_validate_extensions'][0])) {
// Build the list of non-munged extensions if the caller provided them.
$extensions = $validators['file_validate_extensions'][0];
}
Saves to the DB
if ($file = file_save($file)) {
Prints messages to the screen
if ($file->destination === FALSE) {
drupal_set_message(t('The file %source could not be uploaded because a file by that name already exists in the destination %directory.', array('%source' => $source, '%directory' => $destination)), 'error');
return FALSE;
}
Writes to the disk
if (!move_uploaded_file($_FILES['files']['tmp_name'][$source], $file->uri)) {
Sets permissions on the disk
// Set the permissions on the new file.
drupal_chmod($file->uri);
Could we shove any more stuff in here?
Some ideas:
- Let's have it also send emails with the files as