The purpose of a lease is

1. to list all expenses you will have when renting

2. for applying for an apartment

3. to protect both the renter and the property manager

4. to get a credit report to show you will be a trustworthy renter

I believe it is 3. protect renter and property manager

A lease is used to law down the law pretty much. It tells you how much you're paying, why you're paying, how to pay, and all rules attached it is a contract that can last from 1 month to 36 months. If the renter messes up the owner can show the lease and the rule and kick them out. But also if they include that the property manager will fix any leaks and they aren't the renter can threaten eviction and legal consequences. Both sides are protected legally.

answer; code of federal regulations;