Belts and hoses are an important part of a car's engine system and they play a critical role in ensuring the smooth functioning of the vehicle. Over time, belts and hoses can become worn out and damaged due to normal wear and tear or exposure to extreme temperatures, which can lead to a number of problems.

Here are some reasons why belts and hoses need to be replaced on cars:

1. Wear and Tear: Belts and hoses are made of rubber, which can deteriorate over time. As a result, they can develop cracks, become brittle, and eventually break.
2. Leaks: Hoses can develop leaks due to wear and tear, which can cause coolant or other fluids to leak from the engine, leading to overheating or other problems.
3. Tension Loss: Belts can become loose over time, which can cause them to slip or break, leading to engine damage.
4. Preventative Maintenance: Replacing belts and hoses at regular intervals, as recommended by the manufacturer, can help prevent breakdowns and costly repairs.

Overall, replacing belts and hoses on a regular basis is an important part of vehicle maintenance and can help ensure the longevity and reliability of your car's engine.