When you buy a property with the intent to rent it out as a landlord you are likely doing it to make money. While the landlord stereotypes of a businessperson that is willing to do anything to make a buck off of their poor, unsuspecting tenant is usually far from the truth, that doesn't mean that you're in the business for anything less than a profit. You want to fill your properties with tenants that will pay their rent on time and take care of the home as if they were paying the mortgage on it.
Empty properties cost money. Firstly, they're not bringing anything in. Even if you've paid off the mortgage on the property already, you're paying taxes on it and possibly even a few utilities so that nothing overheats or freezes, causing more trouble than a few extra dollars would be worth. An empty property may be broken into if a vandal sees it vacant for a length of time and the clean up could be extensive, pushing back your hopes of filling it even further.
You should never allow your screening policies to slacken when you're having trouble filling a property, but there are other ways that you might want to consider if you find yourself in this position. Take a look at the surrounding area's rent. If other properties about the same size as yours are going for quite a bit lower every month, you're going to have trouble renting yours out unless you have some major perks that go along with it. You might even want to consider dipping your price just a little below the others. Don't drop it too low, though, or potential tenants will think something is wrong with the property.
It's a fine balance in making sure your property doesn't remain vacant and that you choose the right tenant for it. Check out these tips for keeping your vacancies low