Do you have to place the tenant's security deposit into an escrow account? If so, why?

yes....but you don't need a segregated escrow account....a reciept is fine....you don't even need to keep it....just have to pay it back when they move

That depends on what state you are in. In most, no. If you do, it's so you don't spend it and it's guaranteed to be there, because it is NOT the LL's money, it belongs to the tenant.

That is what the law says in my state. That is not your money to spend, it is a deposit which you are expected to return unless the terms of the lease are violated and the place is damaged beyond normal wear and tear. It must be available when the renter vacates and paid in a timely manner.

That is required in some states but not all. The states that do require it do so that the landlord does not steal the money.

In some states you do. So it can accrue interest.