One of the main reasons why someone would go with soy-based insulation is the safety factor, it contains no formaldehyde or urea. Also, it will not emit harmful gases during its application. This is because it is applied with a water-based spray which doesn't any hydrofluorocarbons or other harmful gases.
Besides these health benefits, soy-based insulation has great energy saving and sound dampening properties and it won't degrade or decompose.
Another reason that may motivate you to consider this type of insulation is the fact that soy is a renewable resource and can support local farming as opposed to the use of fossil fuels.
While looking at different types of insulation it is good to remember that any type of spray foam will be friendlier to the environment than fiberglass just because of the energy-saving advantages that it has over batt insulations.
So while considering your home and its energy-saving facets, adding soy-based insulation to the equation may make sense.