The search for a single-family home can occasionally seem like a giant maze that doesn't end. How many stories? HOA or not? Which part of town? How many bedrooms? Those and many more questions all have to be decided by you and your family to ensure you find the home that is best suited to your needs. One of those questions is whether or not you want a home that has an accessory dwelling attached—a casita, guest apartment, granny flat, or some other extra space that could be used as a separate dwelling. For many people, these units are great additions. You should be aware of a couple of issues first.
Potential Rental Income
One of the biggest benefits to having these extra spaces is that you can rent them out. You get the extra income, someone gets relatively independent housing, and for the most part, everyone's happy as long as the tenant is quiet and does not create issues for the neighborhood.
One caveat is that in some cities, these extra units are actually illegal to rent out to unrelated people. In other words, they might have been built long ago to house a homeowner's parent, but not a random student. A few localities have amended these laws in order to ease housing crises, so check local laws first if you hope to rent the space out.
Extra Office Space
Another advantage is that you have separate space for a home office. If you do freelance work or telecommute, these spaces can give you more room to spread out. The space also provides a buffer between you and family members who might otherwise keep interrupting if you were working just down the hallway.
Less Yard Space
On the negative side is the fact that some of these units take away yard space. Units over the garage don't, but a casita out front (like you find on a lot of new-build houses in planned developments) or a pool house in back takes up ground space. Be sure you're OK with that because if a big, unimpeded yard space was something you wanted, you'll have to ensure the unit doesn't interfere with that want.
Talk to your real estate agent about these units and see what experiences the agent knows about—he or she should know about local laws regarding using them as rentals, and whether there are homes for sale that have large yards in addition to these dwellings.