Climbing harnesses are probably the most important of all safety equipment. The belay loop is just a small band of (heavily reinforced!) material but it's always a crucial component in the rope system, and the fit and style of harness will go a long way towards determining how comfortable you are when on belay for long periods, how you sit when rappelling or on a hanging belay, and how clean and painless your falls are. Nobody who has taken a fall in an old-fashioned, early model sit harness ever wants to let go of their lightweight, modern, comfortable one. A climbing harness is usually the second piece of gear a novice climber buys and there might be no need to worry about upgrading for years to come. It takes far longer for a harness to wear out than a pair of shoes, which may go at the toes within a season or two if you climb frequently. But that doesn't mean you shouldn't change your harness every two or three years at least. Like all soft goods they will weaken over time. If yours looks battered and the belay loop is fluffy it's time to invest in a new one.