Crimes are primarily used to grow levels, or to gain a quick bit of cash.
The harder the crime (more nerve it uses) the better the cash income but they are much harder and don't try doing them straight away or you will end up in jail or hospital
There are many types of crime... Search for cash, GTA or even hacking. Some crimes require certain items such as a coat hanger for the GTA or a gas can for the Arson.
Some items you will receive from the crime, like a car from a GTA or rings from theft. Some you will receive cash. Be warned: The more nerve is used for a crime the more expensive the item or the more money you will get but failing will cause your exp to drop this is an unforeseeable thing, but is very important. The higher your exp bar the harder crimes you can do, It also leads to growing levels. See nerve.
Submitted by AAHH