For me the decision to use poles or not is based far more on the terrain and the trail than my pack weight. I do not need them for general balance or to protect my knees (yet). They come in most handy for me during creek crossings and on especially steep or rocky trails. Loose rock is the worst! I find that one pole is usually enough to assist in those situations.

Many of the trails I hike are narrow and have brush impinging on the trail for a significant percentage of the distance. Under those circumstances the poles are constantly impeded by the brush and simply get in my way.

Pika, a couple of years ago I listened to an interview with a gerontologist about old people falling. The most interesting piece of it for me was his explanation that there is a time lag between the feedback we get from our leg muscles and when that information reaches our brains to be processed and a further lag in the opposite direction as the brain sends out control signals. When we first learn to walk, we train our brains to expect that lag and to compensate for it.

As we age, the lag increases, but our brains tend to be less elastic and often hang onto the expectations that always worked in the past about how long the lag should be. The result is that our nervous system can get out synchronicity between our legs and brains, causing stumbles and falls.