Every house in the western world has gutters of some kind. From angled flat rooves with drip opening to large mansions with dozens of roof sections. Every surface that can be rained on must have suitable a suitable way of getting rid of that water, fast. If not then that water can sit and sitting water is a danger. It can bring mosquitoes in the summer and can freeze and break your gutters clean off in the winter from the sheer weight of the ice. There is nothing that can be done about this, even specially designed gutters made with the express purpose of preventing blockages and detritus from getting in cannot prevent all forms of blocks and its better to have a gutter you can clean than a closed rain gutter you cannot access.
A clogged gutter is dangerous for your entire home. Strangely enough, as it sounds, houses are not built to be waterproof. They essentially cannot be as they need to breathe the air outside so it can enter the attic and travel through vents, insuring your home never smells damp or mouldy like houses from ages past. Houses have many entryways for air to travel from roof vents to gable vents to ridge vents and most importantly in the case of gutters, facia vents. Facia is the edge of the roof. It is often raw wood or painted and contains hundreds of tiny holes called facia vents. These holes are cut into the food that is installed at the roof edge and allows the attic to breathe from the bottom as well as the top. Without facia and soffit vents your attic will not breathe properly.
If you have a blocked gutter then the water that gathers and spills over will get into your facia vents and wet the insulation in the attic. This can lead to roof leaks and mould. If not dealt with quickly your home could end up needing tens of thousands of dollars in repairs. If this goes on for a whole season you will certainly have to replace your roof. That is not all though. A non-functional gutter can lead to foundation damage that can cost even more to repair. As the waterfalls and collects at the side of the house it will sink into the ground and wear away the foundation. That is the reason gutters tend to end far from the structure of the house so the water can flow into a storm drain or the ground through gravel. If the water continues to pool and the gutter is never unblocked then your house can start to fall apart.
So make sure you get your gutters cleaned and repaired regularly. They may be the most important part of your home. Caring for them will keep your house and roof and attic in good condition for the long haul. Having to replace a roof and insulation sooner than you have to can be a life effecting event that can lead to financial issues that you may not get out of for years, maybe even decades. So keep your gutters clear and make sure no water spills over and that the spout is directed somewhere safe and away from the structure.