Outdoor space is something that is almost always wanted. While in some areas it cannot be expected for most price points, it is certainly something that people do generally want. In largely urban or developed areas, outdoor space is often only a distant dream to most people. If, however, you are renting in a rural area, this will not be a concern for your renters. It will be expected. This is what I meant when I stated that some people will not find use in this list.
Some renters will feel a large need for usable outdoor space. This may be due to children, animals, or even something like claustrophobia. If you have yard space that the tenant may use, you may want to think about possibly installing a fence. Again, though, learn your town's bylaws and always remember to check to see if you need a permit for a fence, especially of a certain height.
Even if outdoor space doesn't mean a full yard to some people, it can still be nice to have access to a small patio or balcony if the apartment is on an upper level. Being able to have a chair or two, maybe even a small table, outside to drink coffee, read a book, or maybe even grill can be a wonderful feeling for a renter. It also provides a good space for anything that needs open ventilation, such as painting or cleaning with potent chemicals.
Having an outdoor space, if possible, is always a good idea if you are trying to rent an area out. Even if you simply build a platform for your resident outside that they are allowed to use, it can be a great selling point. If this is something that is wanted in your area, look into the different possibilities.