Rome wasn't built in a day, and your criminal empire wasn't either. It took the money of hard-working people to build it, and now, there is another type to extort.
Your whole Empire of Sin would mean nothing without customers coming through the doors and spending their money in it. With the introduction of Precincts, there is a new customer model. Each Precinct has a small number of customers. Building rackets in a Precinct means that more customers will become available. However, if a Precinct gets too crowded and there are too many options available, customer growth will be slow.
Each racket type plays a role in garnering more customers for you. Speakeasies are the workhorse for your empire, bringing in the main source of your income. Casinos, with all their flashy lights and promises of wealth, lure customers to your Precincts. Brothels help to grow the customer base for the Precinct.
As you upgrade your rackets, the number of customers will increase, as people are drawn to swankier places and the option of a better quality of alcohol. However, if not managed wisely, your Precinct could end up with negative customer growth. If the Police Activity number gets too high and their presence is felt around the Precinct, people are less likely to indulge their vices. What’s more, if you have a busy Precinct, you need to serve good quality alcohol to entice more customers in.
Loan Sharks can also lower your customer growth. Though they are a good source of revenue, people who are struggling to repay you are not likely to spend any spare cash in the pub. Like any other racket, they increase criminal activity and so the cops cannot ignore them forever. It’s all a balance, to fine-tune and perfect so that your empire comes out on top.