Couches should be vacuumed as often as carpets are to remove surface debris, but, just like carpets, they also need deep cleaning from time to time. The frequency you have your couch deep-cleaned depends on how frequently it’s used. A family of five that spends all its time in the living room will need to clean the couch more often than a single person who rarely uses it.
Professional cleaning should generally be done at least every other year, but go ahead and move that timetable up if it’s beginning to smell musty or if you frequently have pets and children climbing all over the furniture.