diff --git a/tests/scripts/delete_old_courses.php b/tests/scripts/delete_old_courses.php
index 8bf1011450..93f79664cb 100644
--- a/tests/scripts/delete_old_courses.php
+++ b/tests/scripts/delete_old_courses.php
@@ -1,8 +1,15 @@
 <?php
 /**
- * This script synchronize the exercise score (track_e_exercises.exe_result)
- * with the LP score result (lp_item_view.score).
- * This script works only if 1 there's one attempt
+ * This deletes courses that were created but no file was ever uploaded, and
+ * that were created previous to a specific date and last used previous to
+ * another specific date (see $creation and $access)
+ * Use this script with caution, as it will completely remove any trace of the
+ * deleted courses.
+ * Please note that this is not written with the inclusion of the concept ot
+ * sessions. As such, it might delete courses but leave the course reference
+ * in the session, which would cause issues.
+ * Launch from the command line.
+ * Usage: php delete_old_courses.php
  */
 
 exit;
@@ -35,6 +42,8 @@ if (!empty($items)) {
     foreach ($items as $item) {
         $size = exec('du -sh '.__DIR__.'/../../courses/'.$item['directory']);
         echo "Course ".$item['code'].'('.$item['id'].') created on '.$item['creation_date'].' and last used on '.$item['last_visit'].' uses '.substr($size, 0, 8).PHP_EOL;
+        // Check if it's 160K or 9.1M in size, which is the case for 'empty'
+        // courses (created without or with example content)
         if (substr($size, 0, 4) == '160K' or substr($size, 0, 4) == '9,1M') {
             CourseManager::delete_course($item['code']);
             // The normal procedure moves the course directory to archive, so
@@ -51,9 +60,11 @@ if (!empty($items)) {
             }
             $count ++;
             if ($count%100 == 0) {
+                // Print progressive information about the freed space
                 echo '### Until now: '.$total.'K in '.$count.' courses'.PHP_EOL;
             }
         }
     }
 }
+// Print final information about the freed space
 echo $total.'K in '.$count.' courses'.PHP_EOL;