Why you ask? Well, there is the distinct, non-zero probability it will never get there. Who knows why? Not the USPS. The other, perhaps more important reason is the cost. Certified mail with return receipt for a 9x12 envelope with three pages will cost almost $15. UPS ground is a little over $12.50 for the same envelope with over 30 pages. With both you will get a tracking number, and while you will not get a return receipt with UPS, you are far less likely to need it, and with USPS return receipt you have to have faith they can actually deliver. That is far from certain. There is also the issue of time. USPS delivery of regular mail between Decatur and Dunwoody can take two weeks. UPS gets it there in two days.
So, if you think you need certified mail, reconsider. Stick with the pros.