Is the "size" field in file_managed used for anything?
It's used in a few places:


theme_file_link() where it's used to add microformat data to a file link (per http://microformats.org/wiki/file-format-examples).
file_space_used() where it's used to "determine total disk space used by a single user or the whole filesystem".
file_validate_size() where it's used to "check that the file's size is below certain limits".


It's probably a good idea to fill this field in if you're able, or at least run a small script to do so after you've manually entered the records. Something like this maybe:

// The filesize column defaults to 0 so it's an easy check.
$fids = db_query('SELECT fid FROM {file_managed} WHERE filesize = 0')-&gt;fetchCol();

// Loop through the files and update the file size field.
foreach (file_load_multiple($fids) as $file) {
  $file-&gt;filesize = filesize($file-&gt;uri);
  file_save($file);
}