How do Sunhemp or guar help in crop production management? How is it better than fertilizers?

(N/A) Sunhemp or guar are grown and mulched by ploughing them into the soil prior to sowing of the crop seeds.
These plants act as green manure,which helps in enriching the soil with nitrogen and phosphorus.
They are better than chemical fertilizers because they do not destroy the natural soil fertility over time.
Additionally,they do not cause soil or water pollution,making them an eco-friendly alternative to synthetic fertilizers.