1. Tenant Safety. Often, if a tenant does not have funding they will attempt to purchase cheap things and this may include appliances. Old or cheap appliances like microwaves and air conditioners are often safety issues due to exposed wiring or simple overuse. If you furnish the apartment, you know that your tenant (and your property) are relatively safe.
2. Tenant Comfort. A comfortable tenant is a happy tenant. For someone who is coming to your property with very little often has a heck of a story as to how they came to have very little. Often, these are abuse victims or people who have lost everything in some kind of natural disaster. If you are able to provide them with some form of comfort, then that will make them more likely to stay with you for an extended period of time.
1. Moving. If your tenant shows up and says that they do not need furniture, then you will need to move everything out of the apartment. This is often at least a full day of work and you can't always afford to take that. This is even more difficult when the apartment is on an upper floor or if you don't have people that can help you move.
2. Storage. Let's face it, storage of an entire apartment of furniture is not small. Either it will take up a lot of space at your home or you will spend money on a storage unit. Either way, it is inconvenient.
At the end of the day, it is your choice whether or not you offer furniture for your tenants. It is always a good idea to look at the area you are in and the tenants you are renting towards. You never know how much it may help someone.