Why playing as different characters?
Last time I showed you that the sidequests are going to be different for every character. So basically you already know the answer to the title question. But that's only the tip of the iceberg. There is much more difference and I'am going to tell you about it.
The main reason is that playing the game through you will see just a quarter of it. Every player finds his own way to the final. For sure, there are spots where their paths are crossing – as they're staying at the same hotel. But anyway, we did create a lot of unique scenes for everyone. Some of them are permanent some of them are not. So if you passed the game to the end it doesn't mean you've seen absolutely all.
There's one more reason, it is less obvious, but I love it. The point is that playing as different characters helps you understand their motives and personalities better; it will help you to see hidden meanings of their actions. For example, while playing as Paul you will have to do some favors for Rita. It may seem usual, but when you play as Rita you will see the reason she asked him to do it. It means that when you have played it as every character you would see the whole picture.