Well, they get jobs, drivers licenses, food stamps, family aid, medical treatment, buy vehicles, rent houses and apartments.
That there is someone who will devise a way to fraud the system , allowing them to vote, is not a giant leap.
When I lived in southern Arizona, I became friends with a lady who worked with the border patrol. Many might not be aware of this, but when they are caught entering illegally, they are given water, first aid if needed, fresh clothing if needed, and supplies for infants and small children. In addition, they are given some US coins to use in the food vending machines.
One illegal woman was so distraught at the poor selection in the machines that she threatened to SUE for "inhumane treatment". True story.