I've been doing it for 2 years. It's just one of the things I do to simplify the whole process. My oils are pre-mixed and weighed out, lye solution is pre-mixed. When I need to make soap, I place a container of oils in the micro to melt, weigh out the lye solution, get everything ready. Pour melted oils into soaping bucket and place on the scale, add FO,CMP or other additives and it is ready to go! It takes me less than 10 minutes to make a batch of soap. Adding the FO to the oils lessens the chance that it will be forgotten. If it is a new FO and begins to rice or accelerate you still have time to get it in the mold. It doesn't make any difference in the strength of the fragrance in the finished soap