On a daily basis, your home is where your heart is and where you take of your shoes in the evening. As to the house itself, it's an architectural design which functions through the use of layers which each rely on the other to function properly and protect you from the elements. When any one layer suffers a fundamental failure, other parts can compensate, but the failure needs to be repaired as it also puts extra stress on other parts of your house's design structure.
Your roof takes the brunt of the weather, whether harsh sun and thunderstorms in the summer or freezing rain and snow in the winter. Assuming you conduct routine maintenance and repairs as needed, the roof is designed to handle the weather in your area and will move the excess water away so it can be properly dispensed.
The water then moves to your gutters, which are designed with the use of downspouts to put the water in a safe place rather than allowing it to drain into your lawn by the house unpredictably or worse, add more water than your foundation was intended to handle. Where the downspouts eventually take the water varies according to each house and lot, but you can generally trust that when the gutters are functioning properly without sagging the water is going where it needs to be.
Siding protects your home from outside weather as well, but only from outside weather. If the roof and gutters are damaged, water is likely coming inside your walls, and the siding was not designed to protect your house from that direction. Furthermore, if siding is compromised water can get in and swell the walls, in turn causing damage to the roof and gutters.
Without windows, you would be living in a box. You need windows to view the outside world and allow fresh air in on nice days when you can open them, and yet expect them to provide secure insulation so you aren't, as Grandpa used to say, heating and cooling the entire neighborhood. Again, failure of the roof or siding causes unnecessary stress on the windows, they all work together as a system.
The bottom line is that when something goes wrong, no matter how minor it seems, you need to have it fixed. Everything works together, nothing ever fixes itself, and problems only get worse (and more expensive) when you put off repairs.