The spread in cookies and biscuits can be caused by numerous ingredients and processing steps. Probably most baking people will know that the amount and type of fat used in the formulation of the cookies plays an important role: the softer (or more liquid/ easier melting) fat more spread can take place and in combination with that the dosage or proportion with the other ingredients.
The amount of sugar might be known to many as well, but what about the type of sugar or the crystal size? The crystal size makes a huge difference: compare powdered sugar vs castor sugar vs decoration sugar. The finer the crystal the more spread a product gets during baking. Another cause could be the type of sugar: if you are using syrups such as honey, invertsugar syrup, glucose syrups with higher DE or the more simpler sugars such as dextrose (glucose) or fructose, you can witness more spread as well.
From a formulators perspective the amount liquids (eggs, water, milk) will determine as well how soft the cookie dough will be and will contribute to more spread if the proportions of liquids are higher. In the processing we can control the temperature of the dough by introduction of a resting or cooling time as a higher temperature will contribute as well to more spread of the cookie.
On our education platform we have at the moment 2 different levels of self paced courses for cookies and biscuits: an introduction level (for those who have never baked before) and an intermediate level (for those that have some experience).