It is common for us to park our cars indoors, which protects it from the harsh environment. You would only need a couple of waxing sessions a year to protect the fine paint job on it. However, if your car is exposed to the harsh elements: rain, hail or even battering wind, or if it just spends most of its time outdoors, you should probably wax it every three to four months.
Not only does wax give your car a gleaming radiance, it provides an extra layer of protection against harsh weather, bird droppings, tree sap, ultraviolet rays, vehicular and industrial pollution, and other various grime found in the air and on roads. Waxing your car regularly would prevent these eroding substances from damaging the clear coat: the finish on top that seals the paint, and stop from exposing the paint below. On top of that, if you have to rub and scrub an un-waxed car to clean it, you risk chafing through the clear coat and into the paint.
Washing your car regularly would stave away much of the regular contaminants, but some, such as bug splatters and tar, can require additional efforts to remove. Whether you do it yourself or hire someone, thoroughly cleaning the exterior and applying a good-quality wax by hand at least twice a year can make the paint in your car appear brand new, like the day you bought it.
Rust isn't nearly as common on cars as it was 30 years ago, but it is still the silent killer if you let water or other corrosive materials to accumulate. Driving in Bangladesh, where most roads are unpaved, and puddles seems to appear out of nowhere, being battered by sand water and small pebbles is a common scenario. If you live near an ocean, or a place where the water itself is salty, the best remedy for protecting your car from salt damage is to get it washed on a regular basis, such as weekly. Even if it hasn't rained, there is still salt residue on the roads that winds up on your car, especially underneath on brake, suspension, and other parts not easily visible or accessible.
Though some vehicle owners avoid car washes because of the cost it bears, most car washes give the bottom of vehicles a good cleaning, so minerals and road dirt doesn't build up and cause corrosion.