It used to be taboo to put a rug over carpet, for a lot of people it just didn't make sense. But now decorating has taken a new turn and it's perfectly acceptable to put a floor rug over carpet in a room. In my family it's done all the time.
Why would we do that? Maybe you're in a rental and need to hide ugly carpet but can't remove it. Maybe you have pets or children and want to protect the carpet underneath from stains and spills. Maybe there's a high traffic area that needs a rug to keep the carpet from being excessively worn. There are many reason to put a rug over carpet. And if you ever move you can take that rug with you to help coordinate the decor in your new home.
Floor rugs are most often used to beautify a room, or to lend an extra dimension to a design theme. By choosing the right rug, you can bring together everything from your furniture and wall hangings to the paint and ceiling color. Rugs are made from a huge variety of material, the most common being wool, cotton, polyblends, silk, and even bamboo.
Rug prices vary considerably. The low end versions are less than $100, all the way to several thousand. I'm amazed whenever I see 6 x 8 area rugs selling for $15,000 but I'm guessing they have buyers or they wouldn't be in business anymore. The hallmark of a cheap rug is when the edges curl or fray. There's nothing more annoying and sometimes it can be very dangerous if people trip on them. Rugs can be custom made to your exact specifications and of course they cost a fortune.
There are as many rug designs and styles are there are for carpeting. Possibly more since many rugs are hand made and automatically become one of a kind. It's very common to find a Turkish rug store on a cruise port catering to wealthy tourists who want to avoid local taxes in their country.