Well, the backstories kinda serve a purpose for ABR characters. It allows us to see the character in their own light, so that we will be able to interact with them in the actual comic more effectively. So that we might write for them, if at least for just a response to a question.
I don't really see the purpose of building a backstory if you aren't, or don't plan to be in, a collaberative comic. Or have already created several comics already and wish to show the character's motivation.