That they can make any place homely. As I was walking through a shopping mall in london earlier this week I walked past a large rug with chairs and coffee tables on. The scene, with small children playing with their parents and another couple snuggled up together on a sofa made it feel like I was looking through someones window to a living room. It felt rather strange and surreal but then again very homey and welcoming.
I think that if the large shaped rug was not there then it wouldn't have given me this impression, instead it would of just looked like randomly place furniture in a shopping centre. I believe that the rug and comfy chairs are a nice relief from the hard marble floor and glass ceilings that most shopping centres have.
In conclusion I like rugs because they can make people instantly feel at home.