It’s important to clarify the difference between a security deposit and advance payment of rent. A security deposit is given from a tenant to the landlord to be held in the event there is damage to the property, caused by the tenant.
Advance payment of rent equal to a full or partial month is sometimes collected, to assure the landlord will receive the final month’s rent when the tenant vacates. A security deposit cannot be used by the tenant for that last month’s rent.
The tenant needs to pay the rent on time (or risk being in default of the terms of the lease). The security deposit is then returned to the tenant (the terms of that are addressed by the lease and by state laws).