Ok I have been wondering this since I saw the movie in theaters....

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It seems to me that Harvey Dent didn't get much screen time as Two Face. Is there a particular reason for this? Like, I know Harvey Dent obviously had a huge role, but HD as Two Face didn't get screen time until the end. I guess maybe when I watched it in theaters, and I'm watching it again, I don't quite understand the reasoning to do this. Is it because the main villain is supposed to be The Joker? Maybe when I was younger I always thought Two Face was a major villain and that's not the case? Maybe there is no good reason and it's just 'cause of screen time?

I'm sure I could look this up but I'd rather someone just tell me.