If you have furniture you are planning on keeping, periodic professional cleaning is recommended. However, be careful on who you hire. Furniture designs and styles have different degrees of difficulty in cleaning based on the types of corners, edges and firmness of the upholstery. Also, upholstery uses many different types of fabrics ranging from natural materials like silk to synthetics like nylon as well as the new micro-fiber materials. Hiring a cleaner with skill and experience who knows what they are doing is important. For example, if silk is not cleaned properly, you have the potential for splotching or streaking to occur. Also, if not cleaned properly, white furniture, especially cottons and wools, can turn brown.
While cleaning is typically for appearance, if done properly, it also gets imbedded dirt out of the fabric. It is like your clothes, even though they may not look dirty, you still wash them after use to remove the dirt and soil.