Autism Speaksgives a great explanation of the purpose and uses of visual aids. According to them, "A visual support refers to using a picture or other visual item to communicate with a child who has difficulty understanding or using language."
They continue to explain that the advantages of visual supports are:
They reduce anxiety when routines change: Some children with ASD become anxious when their routines change or they are in unfamiliar situations. Visuals can help them understand what to expect and will happen next and also reduce anxiety. Visuals can help them pay attention to important details and help them cope with change.
They help parents communicate better with their child: Children in the spectrum may not understand social cues as they interact with others in daily activities. They may not grasp social expectations, like how to start a conversation, how to respond when others make social approaches, or how to change behavior based on unspoken social rules.
They help their child communicate better with others: Children with ASD often find it difficult to understand and follow spoken instructions. They may not be able to express well what they want or need. Visuals can help parents communicate what they expect. This decreases frustration and may help decrease problem behaviors that result from difficulty communicating.