Keeping kitchens clean is an important step in preventing food poisoning. There are many reasons for cleaning but the most important reason is to ensure that all surfaces and equipment that come into contact with food are not contaminated with food poisoning bacteria.
All food and hand contact surfaces should be disinfected / sanitised. This includes work surfaces, chopping boards, knives, slicers (food contact surfaces) and door handles, fridge handles, light switches taps etc (hand contact surfaces).
Cleaning is the removal of food residues, dirt, grease and other undesirable debris. This requires physical energy (elbow grease!), heat and/or chemicals (detergents). Cleaning only removes dirt from the surface but does not kill all bacteria.
Disinfection is the reduction in levels of bacteria to a safe level. This is usually done by the use of chemicals such as disinfectants and sanitizers, intended for food use; or by heat (hot water around 82°C or steam).