Money is a privative: if you've got lots of it, you hardly notice it's there, but when it's all gone, nothing else could matter to you more. It's the oil that lubricates the machinery of Western culture, making everything spin around that much more easily, but crushing a lot of us in the process. From the outset of designing this game, there was no doubt that money would be of central interest to the characters: they all want more of it, but just as importantly, they don't want to run out of it. The straightforward way to handle this would have been to work out how much everything cost in the game (including the living expenses for each of the characters) and then award the PCs money for doing certain things, especially any jobs supported by their playbooks. With that information in place, the game's economy would have taken care of itself and there would have been very clear markers for what each character could afford to do next.
I didn't do that for a couple of very good reasons, the first and foremost being that I play storygames to have fun and explore the lives of the characters in a given set of situations, not to simulate real-life to the finest degree; I really have a strong aversion to excessive bean-counting in RPGs, so a realistic money mechanic was as attractive to me as one for tracking how hungry the characters were, how many calories they got from what they ate and when they should take a dump.
The second reason I decided against an income & expenses-style model was that if you give players a score to track, someone will immediately see that as the way to 'win' and will look for ways to game the system to do so. I also wasn't confident in my ability to keep a detailed economy balanced and was aware that, not only could one big payoff upset the apple-cart, but a series of smaller payoffs plus any overlooked or underestimated expenses would have the same result. It looked like a headache to crunch the numbers and my personal rule for game design is that it shouldn't give me a headache, so there was never going to be any chance of a system like this being used in The 'Hood.
One idea I seriously toyed with for a while was not to have any mechanical representation of wealth or money in the game, but to handle it all narratively: purchases and expenses could be handwaved ("Well, sure, you've had no problem with your business this week, so you can afford to buy a round of drinks") and any big payoffs would just reposition the character in the narrative, giving them more leverage in situations involving money but also making them a bigger, juicier fish to be caught and gutted.
After an involved and detailed exchange on this subject with DWeird on the Barf Forth Apocalyptica forums, during which I considered using dough as a stat you rolled against to get things done like buying stuff, I gravitated back towards a more abstract representation of how much money you had but with the addition of the concepts of getting by and being short. Now it's time to put my hands up and confess how my love of wordplay and my inability to come up with lists of 'Looks' for all the playbooks contributed to this decision: when it became apparent that the characters should be concerned with protecting their livelihoods, I thought of the idea of each playbook having a unique revenue stream that could be threatened by outside events. There were a few instances of this which were immediately obvious and which had already crept into some of the playbooks, such as mention in the Feelgood's moves of interrupting their supply of drugs, so I latched onto the idea and looked for a way to formalise it in the rules. Each playbook would need a separate entry for this, just as each one has a separate entry for sex moves in Apocalypse World and Monsterhearts, so I looked at the design I had roughed out, trying to spot a place to put in a statement about how the character earned their living... and there was the word 'Looks' staring up at me from a space that was nearly blank as I was struggling to fill it. Something in the back of my mind popped up with the word 'Loot' as an appropriate substitution and the principle of protecting your livelihood became part of the hack forevermore; I still find it a challenge writing an appropriate Loot entry for each new playbook (I'm doing that a lot at the moment...) but it's much less work for me than coming up with lists of Looks for each one!
Finalising the rules for dough was a much harder, longer road, with lots of false starts and dead ends along the way, as there were two driving factors to contend with: the need to mark the character's level of wealth within the game versus my own preference for keeping things at a story level rather than a mechanistic one. A recent campaign I'd run for a few friends was strongly influencing my thinking: we'd played the worlds first Dead of Night campaign and, despite having absolutely no way of tracking wealth or status in the game, one of the characters had risen from a petty criminal to Pope of a new religion within the space of 8 weeks of play, all as a result of the narrative path we'd followed, taking the consequences of each scene and building on them episode by episode. I really enjoyed that and wanted to provide the same space for stories to take place within my hack; I didn't want the rules to restrict the stories we could tell about the characters and felt that no-one should reach a point where they couldn't take the next logical step in their character's development because the rules counter-indicated it.
In the end, it took about two weeks of private thought and public discussion on the subject before I settled on the almost-abstract treatment of dough as it is now: I was much happier to use it as an indicator of your general level of wealth than as an exact count of your money. There's no hard and fast correlation between money and dough because there shouldn't be, they're two different things: dough is about more than the currency in your pocket, its also about your credit cards, your pre-paid mobile contracts, your insurance & investments, your on-going payments on your house and your car... in short, it's about everything that has monetary value in your character's life, not just the money itself. This made it easier to describe how being short affected you: previously, it was hard to reconcile this with having a lot of dough and there was the option to take -1 dough instead of having your livelihood threatened, but the two sides of the economic model still didn't quite line up and there were gaps between them which were creating edge cases that needed more and more spot rulings to patch up.
With the current model, its easier to see how a character with a lot of dough can still be short: sure, you've got all the trappings of wealth, but if you've just paid your bills in anticipation of a big score that actually falls through, then you can have all the perks of a well-off person but still not be able to afford a ride on the bus or do your weekly shop. Dough is about the big money in your life, but protecting your livelihood keeps change in your pockets.