Changing speed is essential to surviving. If you're in an open area, use Speed 3 or 4 to help you maneuver better. This is especially true when you're dealing with smaller, quicker ships. If you're in a tight, enclosed area it's best stay at Speed 2 or 1 to avoid quick movements that can cause you to run into bullets and ships. In general, adjust your speed according to enemies and surroundings.