If you want to ditch the hotel for a more interesting (and possibly cheaper) experience, Airbnb and its ilk can be great. If your host isn't legally allowed to sublet, however, you could end up on the street while visiting a new city.
As Lifehacker alum Adam Dachis explains, if a person is renting their home, they may not be legally allowed to sublet their extra space. In those instances, if the landlord discovers that you're paying to stay there, they have every legal right to evict you. This could seriously screw up your vacation:
While Airbnb offers lots of great places to stay, sometimes the people looking to make an extra buck off their apartment aren't legally allowed to do so. One of my neighbours appears to be doing this and I recently stayed in a place in San Francisco where I forgot to ask and ended up staying somewhere I technically wasn't allowed -- at least according to the friend of the guy renting the place to me. This kind of illegal (or at least somewhat unethical) behaviour doesn't always result in dire consequences, but it can.
Of course, some renters can share their home with the blessings of their landlord. Your host doesn't necessarily need to be the owner. And, of course, there's always the chance that their landlord won't find out during your stay. However, that's a big risk to take, especially if you're planning to visit somewhere far from home.
The One Question You Should Ask Before Booking an Airbnb [Awkward Human]