By walking on well defined tracks the evidence you leave is so minimal only a well trained tracker can tell someone have been through recently. By spreading out when off track each plant and area of ground is only stepped on once, giving it a much better chance to spring back up. Repeated bashings of a plant will result in the plant dying or at least taking longer to recover.
It is believed that one well formed narrow track in the right location has less impact to the environment and visitors experience then many less well formed tracks that zigzag through the bush. Therefore parks management staff plan tracks over terrain in a way to minimise the chance of erosion and impact on flora and fauna, whilst maximising visitors ability to safely access areas of interest.
Walking through puddles of mud means that you end up with muddy boots and a deeper puddle, but the track does not get any wider. Your boots and the puddle will dry up soon, but wide tracks stay wide for many years. In some areas tracks have become very wide from people avoiding puddles. And yes just one person walking around the edge does make a big difference. Sometimes park mangers will build small bridges or duck boards to make travelling through muddy areas better for your socks.
If safe it is better to climb over or remove obstacles from tracks (such as fallen branches) than to walk around them. If you can't remove them safely, notify park operators and they will organise it. Walking around obstacles will widen the track or create a new track.
On tracks where people are likely to come along during a rest break, rest off to the side of the track so that groups do not widen the track by walking around you. It is best to rest on a rock or log or other hard surface to minimise the damage to plants. If it is a quiet track then best to either find a durable surface or rest on the track, but stand up and let other pass if they do come through.
Taking short cuts creates new tracks, and they generally end up point straight down a steep hill. When you take these short cuts you damage the plants that hold soil in place, and next time it rains soil is washed down the hill, and in a over time we end up with an eroded gully. Take the time, it is much safer and better for the environment to walk the extra few meters.
These off track principles apply when in a campsite and you are finding a place to toilet, collect water or fire wood, as well as when you are travelling from point a to b.
The reason to fan out when off track is to minimise the risk of forming a track or scar on the land. When you walk in a line the same plants and ground get stamped on repeatedly in a short time frame meaning that you are much more likely to kill or cause severe damage that may not be obvious immediately but may take many years to recover. If you do form a path then others are more likely to follow and make the problem worse. So fan out, look for durable surfaces to walk on, and make sure that nobody follows you.
Do check with the park rangers when planning a trip through an area with no established tracks. In some areas visitors are not permitted to head off track, this is to protect environments that are so fragile and slow to recover that one foot print may take decades to disappear. So please take “keep to the track” signs seriously.
Ensure that you are paying close attention to your navigation. Needing to backtrack or conduct a search, not only has an impact on moral, but a very significant impact on the environment when you are off track.
Wearing soft shoes whilst walking carefully can help minimise the damage you do to plants. Big and heavy boots may be required sometimes, but do take their toll. Soft shoes have a two way effect, one is that they are softer so that they are more likely to mould to the shape of the plant you step on then to cut or crush the plant. The softer shoes also give better sensation to your feet so that you can feel damage that you may be causing and avoid it.