Milkfat, or fat in general, including that from non0dairy sources, is important to ice cream for the following reasons:
increases the richness of flavour in ice cream (milkfat moreso than non-dairy fats)
produces a characteristic smooth texture by lubricating the palate
helps to give body to the ice cream, due to its role in fat destabilization
aids in good melting properties, also due to its role in fat destabilization
aids in lubricating the freezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment)
The limitations of excessive use of butterfat in a mix include: