The quick answer, YES. And sometimes even more often than once a year.
Here's why ... It's an oil, reality and soil develop up on your carpet fiber. No matter what takes place in your home; soil, dust and dander settle on your carpet. The official living room carpets or the visitor bedroom carpets get minimal traffic but dust is everywhere and it settles nicely into your carpet fibers.
On a side note-- this is why carpet can actually be much better for people with severe allergies than tough surface floor covering. The dust settles into the carpet and isn't floating around. On a hard surface like tile or wood, the dust is easily disturbed and remains more present in the air.
Anyhow, if the soils and oils are not removed, they gradually settle deeper triggering friction and wear in your carpets. The small pieces of soil rub on the fragile carpet fiber and trigger it to break down or make tiny cuts in it. If you let your carpet get to the point where you're seeing soil then it's probably past due and prepared for a steam cleaning.
Most carpet manufacturers recommend a steam cleaning or hot water extraction as soon as a year. Schedule your annual carpet cleaning with one of our professional residential carpet cleaners in your area.