What is the reason for sanitizing dishes utensils and food preparation surfaces?

To avoid "food poisoning" -- which is normally associated with consuming bacteria or toxins such as: Campylobacter, Salmonella, and E Coli.

Sanitation is important to avoid cross-contamination in the food preparation process. For example, if a cook uses a cutting board to both cut raw chicken (before cooking it) and then uses the board to cut vegetables for a salad (without sanitizing the board first), then bacteria such as Salmonella could be transferred from the raw chicken to the salad vegetables. The chicken (assuming it gets cooks thoroughly) should be safe to eat because the bacteria is destroyed, but the salad could make you very sick because of the cross-contamination.