Your question seems to bring me more confusion based on your above post. You state that you’ve never been in a fight that “looked” like a sparring session and that the last time you were in a fight it was hard with no pulled punches and no rules. However, your preferred METHOD of training is one that consists of the MOST rules and considered probably one of the MOST passive training one could perform aside from line drills. Some how I can not make the correlation as to why you choose not to incorporate some sort of free sparring into your training based on your prior experiences.

To address your post more specifically here is how I believe free sparring adds to aid in increasing your effectiveness in a self-defense situation:

1 – Full force blows – Allowing full force blows provides the student with a more realistic feeling of what it will feel like to deliver a full force blow to an opponent and what it feels like to be hit full force from an opponent. Something you should be psychologically prepared for and fully understand in order to avoid the mental cramping and log jam that occurs when adrenaline kicks in during a real life encounter.

2 – A Moving Target – Unlike Yakusoku Kumite and like a realistic encounter your opponent will be able to move AT WILL. Being exposed to this is essential and allows the student to begin strategy on how to corner and limit mobility of an opponent to deliver full force blows.

3 – Timing and Resistance – Yokusoku Kumite does provide some timing training however there is no resistance therefore the student will be unfamiliar as to how much strength and timing would really be required to produce the technique or principal in real time against an opponent bent on taking your face off and not allowing you to fully execute your desired technique. This is essential to understand how to time techniques against someone hell bent on hurting you throwing full force techniques. This is even more important when incorporating throwing techniques.

4 – Pressure Testing Techniques – Techniques and principles of combat work great against a passive opponent. However when introduced to a resisting opponent one will realize that what worked great in Yakusoku Kumite doesn’t seem to either work or does not gain the desired result as easily as it did. This is because now this technique or principle is being utilized against an opponent who is adrenalized, resistant, scrappy and mobile. Thus rearranging your timing, strength and strategy is required to achieve the desired result.

Does sparring have rules? Yes. The amount of rules is based on the instructor’s discretion and goals he/she wants to achieve for their students. Is it more beneficial once the students achieve an understanding of the yakusoku kumite principles, absolutely in my opinion.
"I'm gonna come at you like a spider monkey"