What can cause unnecessary obstructions?

You answered correctly. According to German traffic rules, causing unnecessary obstruction to other road users is prohibited. Stalling the engine in dense traffic, driving significantly slower than necessary without reason, and breaking down due to running out of fuel are all examples of this because they disrupt the flow of traffic and could be avoided with proper attention and preparation. Always ensure your vehicle is maintained, that you have enough fuel, and that you adjust your speed appropriately for the situation to avoid creating unnecessary delays or hazards for others. Recognizing and avoiding such behaviors will help you drive safely and legally on German roads.