Grease – Every time you wash pots or use the dishwasher a certain amount of grease and fat residue will pass into the drainage system. The grease and fat solidify when it cools and starts to coat the internal walls of pipes. Gradually it reduces the internal width of the system, that then reduces flow rate which increases the buildup of grease and fat until everything finally comes to a head and the system blocks. You can, of course, reduce the chances of this by scraping plates into the garbage before washing them.
Roots – The flow of water inside the drain pipes causes vapor to escape into the surrounding soil, usually through a crack in the pipe or a loose joint. The roots are attracted to the opening to reach the plentiful nutrients and moisture inside. Once inside the pipe, the roots will continue to grow, and if not disturbed, they will eventually completely fill the pipe with hair-like root masses. These masses can act as a net as they catch household fats, oils, grease, tissue paper, and other debris discharged from the residence. As roots continue to grow, they expand and exert considerable pressure at the crack or joint where they entered the pipe. The force exerted by the root growth will break the pipe and may result in total collapse of the pipe.