It is if you want to minimize the risk of a breakdown caused by a hose failure. Coolant hoses are pretty rugged, but after four years of service, the incidence of failure rises sharply. That's why many mechanics recommend replacing the hoses every four or five years. It isn't absolutely necessary, but it can greatly reduce the risk of a hose breaking or leaking.
The whole idea behind preventative maintenance is to replace things BEFORE they fail -- ideally just as the component is nearing the end of its normal service. Unfortunately, it's difficult to tell exactly when that point is reached. The original equipment radiator and heater hoses on some vehicles may go eight or ten years without a problem. Then again, they might not.
If your vehicle is more than eight years old and the hoses have never been replaced, you're probably driving on borrowed time. Replacing the hoses would be highly recommended if you're at all concerned about reliable transportation.
Regardless of how frequently (or infrequently, if ever) the hoses are replaced, they should be inspected periodically to check for problems. Any hose that is leaking, age cracked, hard, brittle, mushy-feeling, bulging or otherwise damaged needs to be replaced.
Heat, vibration and internal corrosion are the factors that age the rubber in hoses and eventually make them fail. In many instances, a hose that looks good as new on the outside will be rotten on the inside. This is caused by "electrochemical degradation," and it occurs because the hose, coolant and metal parts of the cooling system form a galvanic cell or battery. The electrochemical reaction that results forms small micro cracks inside the hoses. The cracks allow coolant to penetrate the rubber and weaken the reinforcement. Heat and flexing accelerate the process, and eventually the hose fails from the inside out. The process may take years to occur, or it may happen in a relatively short time (25,000 miles or less) depending on the conditions that are present.
Upper radiator hoses and small diameter bypass hoses tend to be much more vulnerable to this type of internal failure than other hoses. One reason is because these hoses usually carry the hottest coolant. The smaller inside diameter of bypass hoses also seems to accelerate because the coolant is flowing through it at a higher velocity.
Some hose manufacturers are offering a new type of long life hose made of "EPDM" rubber that is highly resistant to internal corrosion. This type of hose is more expensive, but is well worth the extra cost when you consider how much longer it lasts (up to 200,000 miles or more!).