You can add grounding cables, change spark plugs, spark plug wires, points, ignition coil and do things like disable factory traction control and turn off/disable/remove your tire pressure sensors.

For the most part, this section is legacy from older cars where all the tuning was done mechanically (which is a no-no). If you're futzing about in the electrical system, it's probably best to read this section. ECU tuning and flashes are covered in the "Engine and Drivetrain" section though, so anyone itching to reflash the ECU, keep scrolling.