|Art by Wayne Reynolds|
Why am I doing this?
Well, the most obvious answer would be that its fun. Sometimes it's just entertaining to take a concept and see if you can make something enjoyable to play out of it. However, that's not the only reason why I'm doing all of this.
I've mentioned before that I believe a class should have a unique role within the game, something that you really can't achieve with an already existing class. The Swashbuckler concept is a good example of this since you can't really make an adequate version of the concept with the existing options. So, sometimes you want to create a class that will allow your players to utilize this role better.
You might also design a new class to represent a new concept within your campaign setting. For example, let's say your campaign setting possesses a lot of steampunk elements. Since there is this abundance of technology, you decide to design a class built around it. Thus, the Artificer or Gadgetteer is born.
Finally, you might design a class to replace an existing one that you find lackluster or downright broken. For example, you could design a class called the Crusader which is similar to the Paladin, but doesn't require you to be Lawful Good. On the other hand, you might design a revised version of the Monk in the hope of making it less wonky and MAD.
In the end, I guess there are a lot of different reasons why someone might design a new class. Hopefully this post ends up being somewhat coherent and doesn't turn out to be random ramblings.