TL;DR
Benefits and guidance for running on sand.
Benefits and considerations for runners training on sand.
Advantages of sand
This is a common question when discussing a natural training surface with runners. The original article notes that sand is not suitable for everyone: people with lower-back or other back problems may need a different approach.
Benefits
Less impact than asphalt: during a high-mileage training block, sand may provide an alternative to the loads experienced on hard surfaces.
Greater energy expenditure: the article cites studies in which runners training on sand used 1.6 times as much energy as those running on asphalt.
Strength endurance: sand sessions may contribute to strength, running technique and proprioception.