Feeding Brahmanas of pure character is recommended in vedic scriptures. Brahmcharis of ISKCON has taken a voluntary vow to not indulge in worldly matters but read the deep knowledge of Bhagavad Gita and other scriptures and propagate this knowledge. By arranging prasad for the devotees of Krishna, get blessings of many Brahmanas and Lord Krishna himself.
Devoted and pious people feed Sadhus on anniversary, festivals, birthdays or other important days.