practical examples of this, if you’re curious, include the Tūtohu Whakatupua (which declared the Whanganui River and tributaries as a legal entity), the agreement around Mount Taranaki (which grants it legal personhood), and the invalidated Lake Erie Bill of Rights (passed by Toledo, OH and was designed to allow residents to bring lawsuits on behalf of Lake Erie to protect it)
When you get down to it, law, society, what have you, exists for the purpose of making things better for people that could be overlooked or trampled otherwise. Granting legal personhood to nature achieves that in a number of way