A 6 inch cake is the perfect size to make cake accessible on more than just special occasions. Unless you have 12 or more people in your family, a 9 inch cake just doesn't make sense. It's too much cake. Even if you have cake every night, you'll never finish the cake before it goes bad. And if you do, well . . . you shouldn't be eating that much cake.
This is the finished cake (see picture). I went a little nuts with the fondant flowers, but I just got caught up in the spirit of Fall. But, back to my topic.
A 6 inch cake is a more reasonable size for families of 2-5 people. Even for larger families, a 6 inch cake may provide more options, by having two 6 inch cakes of different flavors, because there is no way that a family of 12 all wants the same flavor of cake (go ahead, prove me wrong). As The Physicist points out, "it already has a higher frosting to cake ratio, if you're into that sort of thing". Because they are smaller, they are less work to make. It's easier to experiment with flavor combinations when you aren't committing to a giant cake of licorice pineapple (I don't recommend licorice pineapple). And lastly, they're just so darn cute! Seriously adorable!
Here is an aerial shot of my cake, so you can see more of the fondant flowers. I made roses, calla lilies, mums, hypericum berries, and kinda generic little yellow flowers. This was a first attempt at painting the fondant, after I shaped the flowers and leaves, to give them more depth. Ain't half bad, if I do say so myself.