A radiator is vital to the health of your engine, ensuring that it does not overheat and maintains an optimum operating temperature.
A radiator cools the liquid (coolant) that in turn cools your engine, thereby maintaining the correct operating temperature. A radiator has a large surface area of thin cooling fins and tubes for the liquid to pass through. Over time these can be damaged by stones, filled with dirt and bugs or the plastic tanks attached to most radiators these days can crack with the constant heating and cooling during normal use.
A radiator flush cleans out all the sludge and other containments that accumulate in your cars radiator and engine.
A radiator flush helps to clear this accumulation so that the coolant can flow properly through the radiator and thereby prevent overheating.
Too much or too little coolant, or mixing coolants is almost as bad as no coolant at all and will lead to corrosion of radiators, heads, water pumps etc.
Many people still believe their vehicle doesn't need coolant / antifreeze if they live in areas that don't freeze or their vehicle is kept in a garage.
Not flushing the radiator and adding the correct coolant is the worst thing you do, because while coolant does contain freeze protection it's most important ingredient is corrosion protection and this is good for around two years.
After this period the corrosion protection will have been depleted and unless the system has the coolant together with the contaminants that have accumulated flushed out the system will begin to corrode.