In the urban area the main issues is the large amount of droppings they can produce which damage surfaces. They also carry a range of diseases which can be passed through their droppings.
Their droppings can also damage solar panels.
In rural areas they can cause significant crop damage.
In the natural world, as their name (rock dove) suggests, they tend to nest of cliff faces. Nesting on building ledges is therefore second nature. The will nest in roof areas and anywhere on the outside of buildings as long as its protected from weather.
Removing potential sources of food will make the area less attractive to pigeons, but to prevent nesting on buildings, it is necessary to employ a pest manager to install the necessary exclusion products.