If your paint is left unprotected by a wax or other sealant, then it is at risk. Bugs, acid rain, bird droppings and other corrosive materials can settle into your paint and etch it, causing damage nothing short of repainting can fix.
Car washing is an important part of basic car maintenance dust sand and especially salt can eat away at your car exterior. Other substances like tree sap and bird droppings can eat through the clear coat thus hurting your resale value. You should wash your car at minimum every 2 weeks and detail it once to twice a year depending on the service you get.