Time travel is mostly used as a deus ex machina to solve a problem a writer has written themselves in. Like in HP, the time travel bit is only for students to learn more, not to erase attacks by Voldemort, because reasons. In other words, they could have stopped the death if Harrys parents, but did not want to, because reasons.

I get that if used well and as a consistent plot device, it can work. But in HP, its simply a one-oft drama device. Its boring and lazy writing.

Edit, ah, I see

My Immortal is popularly regarded as one of the worst works of fan fiction ever written