The /tools/cron.php script (can be invoked from command-line or browser) is used to invoke pending tasks (e.g. e-mail sending, database optimizations, etc.). Nature of these tasks require, that them to be executed at 100% to avoid any database corruption or worse. Unfortunately, when invoked from browser it is subject to web server keep alive and timeout restrictions, that can terminate script execution without even warning it upfront.
Solution
Place command-line (CLI) only restriction in script itself and remove browser execution example from that script.