There are several reasons you might find yourself in small claims court.
If you are seeking the rent from a tenant who has moved, or who has been evicted, you will not be able to sue them in housing court. You will have to bring a proceeding in small claims court if the amount is $5,000 or less, or in Civil Court if it is over $5,000.
Landlords may also sue for late charges, washing machine charges, legal fees, etc., as these are often not collectible in housing court.
A tenant may also sue a landlord for damages relating to repairs, or stemming from an eviction, or perhaps due to an injury alleged to have occurred on the property.