You might come across a recipe that requires you to add ghee instead of oil. There isn't a big difference and you can substitute ghee with cooking oil if you prefer.
Ghee is a type of clarified butter that is prepared from cow's milk. Normally, the ghee is made by heating up the butter in a deep pan to avoid spilling. The butter is stirred slowly to avoid remixing the fat. The oil from the butter will eventually separate from the butter.
You will notice that when you cook with butter it will release froth once heated and melted. This froth will be strained so that none of the oil will be wasted and discarded. The leftover oil from the butter will turn into a pale yellow which will be strained to remove any remaining bits and then stored as what is known as ghee.
On the other hand, cooking oil is a neutral and non-polar chemical substance which means that it does not have an electric charge and will not conduct electricity if it is in such a situation. It is also a sticky or greasy liquid when it is exposed to regular temperatures.
The extraction process of oil is dependent on the type of fruit or seed it comes from. For instance, the sunflower seeds are compressed until the liquid gets released. It will also be refined to change the appearance so that it looks like the cooking oil on the shelves. Other cooking oil may also go through processes to change the taste and smell of it thus making it more appealing.
In some cuisines, the type of cooking oil used in the dish is very important. Flavour is important and chefs prefer to achieve unique textures and flavours that are native to their culture.
Ghee is lighter on the stomach because of the way it has been extracted from the butter. There are some people who struggle to digest food because of the viscous properties it may have. With ghee, a person does not have to worry about uncomfortable indigestion.
Cooking oil, however, has properties that can only come from fruits, vegetables and nuts. This means that there are other fats, such as trans fats, that your body needs to maintain a healthy immune system.
Those are the properties and differences between ghee and cooking oil. It is up to you as the chef to decide on which one is best suited to your recipe.