1) A higher value will detect more scenes as a scene change, usually sticking to 10 is fine, you may want to crank it up to 15 or 20 depending of the footage.
2) For real life, it usually better to turn it on, leave on 10 if you don't want to mess with it.
3) It crash if the footage is very long, test it out with a footage of a few seconds, it should show all the frames that a scene change occur (using the sensitity)
4) Thank you, we appreciate the complement. =)