The syncretism of the practices of mainstream Hinduism with the deities of the folk religions have the effect of lending them legitimacy in the eyes of most adherents of the faith, offering them greater influence, attracting more popularity, and also replacing them outright by a foreign deity.
When mainstream Hindu rituals are combined with those from the folk religions, it gives these deities legitimacy for many followers. This combination increases their influence, boosts their popularity, and can also displace them by a foreign deity.