The obvious...the lease has already been mentioned. If you are selling to an investor, having a lease in hand is a bonus. If you are selling in an area where an investor is not the likely target, your typical buyer will make this home their primary residence, then you will have other concerns to address with the tenant. There are a few cases where tenants are helpful and easy to work with, in most cases you will find them reluctant to allow showings, or they will have a lack in care for the property ie. it will be messy during the showing.