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?

Because the concept of "fixed points in time" only matters when the episode needs drama. :p To be fair though, Rose saving her father would affect her own personal timeline and probably cause a major paradox: if he never dies then she wouldn't need to save him in the first place, and then he'd end up getting killed since she wasn't there to save him.