Depending on where you live, letting your front garden grow wild can be an unneccessary problem. In my semi-rural neighbourhood, grass and weeds are everywhere although, over time, more and more people are trying to keep the streetscape a bit tidier. In a subdivision however, I think it would look very ugly to have even one front yard full of tall grass and weeds, environmentally friendly or not. Why not compromise and concentrate on biodiversity in the back yard?