Dogs come in all shapes and sizes. Larger breed are often "working" animals who can perform work-related tasks because of their size. Smaller dogs, sometimes referred to as "toy" or "lap" animals, need less space than larger breeds. People often get them for companionship, as it is easier to take them with you when you places.
Humans have bred dogs to develop specific characteristics, such as size and shape. Modern breeding includes cross-breeds such as Poodles and Labradors to create the "Labradoodle".