Doctor Who - Series 8

So, maybe a bit out of context, but I started watching Doctor Who last week and I think it's awesome. I just watched the episode 8 of season 1 when rose saves her dad and these weird alien flies invade and I need some help from a Doctor Who expert. In every episode, the doctor and Rose changed something major in the earth's history, but nothing happened. Why does saving Rose's father breaks time, when all the other people they saved and the bad guys they defeated didn't do anything to the flow of time?

Easy answer: It's time travel, so don't think too hard about it.

Long answer: Rose's father is one of those events that's not meant to be changed at all because it already happened and is meant to be. By saving her father, it causes a time paradox. The villains are usually not immune to this because usually they are yet to be killed/defeated. If they were already dead then you can't say save them. When they are alive, anything can happen more or less. Of course these time rules aren't super strict, because time travel in itself is already breaking so many rules and is a giant headache on it's own. There WILL be events in Doctor Who where the Doctor is shown to break his own rules of time travel, but it's usually for extreme reasons or purposes. Hint: It usually involves his companion being in mortal danger.