Master Roasts are based on the idea that roasts should be based on previous successful roasts. You may mark a roast as a master roast and then filter the Roast list by choosing View=>Show Master Roasts which is actually show only master roasts. Then pick the roast you want and choose File=>Duplicate Roast.
There is also the idea in this that customers or maybe your wife think about your coffee as the finished product and if they try to order something it's going to be, "Some of that whatever you roasted last Thursday" and not I want a pound of "Ethiopia Dry Process Limu -Nigusie Lemma" roasted to City Plus using your profile for Brazilian coffees.