When fat - loss is your goal you are often in a caloric deficit, usually by a combination of increased training volume and reduced calorie intake. (sciencedrivennutrition.com)
One of the simplest ways to do this is by increasing the number of sets you perform on a given exercise, thereby increasing training volume. (fitnessandpower.com)
There are countless reliable studies which show that increasing training volume directly leads to muscle size gains, so this is not something that needs any further discussion. (fitnessandpower.com)