Most carpets that people buy are meant to be placed on the floor for the purposes of increasing comfort as well as facilitating the creation of quieter home environment at any given point in time. However, it is not entirely heard of for folks to buy a carpet for nothing other than hanging it up on a wall in some way, shape or form. A big part of the reason why that is the case has to do with the fact that some carpets are incredibly expensive, and walking on them would be akin to walking on a hand carved dining table which is to say that it will be immensely disrespectful of the workmanship that went into creating the item in question.
Since your rug is not going to be on the floor, you might assume that you no longer need to think about hiring a carpet cleaning service. That said, you should know that carpets are naturally inclined to gather a lot of dust. Even if the carpet does not gather dirt from your shoes or feet, it will still attract ambient dirt from the air around it.
What this basically means is that you might want to consider having your decorative rug cleaned regardless of whether or not it gets used for foot traffic. In fact, we would go so far as to say that decorative rugs are even more important to be cleaned since they are far more expensive and allowing them to stay dirty might result in their bright and glorious colors getting muted and dull. That would ruin the resale value of the rug and diminish its aesthetic appeal all in all.