There is one, and only one, advantage of having ADS-B OUT. It lets you see your traffic on board with a glass screen cockpit such as the Garmin 1000 or on an IPad.
The main purpose of ADS-B OUT is to let airliners fly more direct to airports thus saving fuel. The problem with this philosophy is that in the US airliners use mostly the same 35 airports. They all want to arrive and depart at the same time, which will lead to delays and holding patterns where arrivals will be backed up.
All airplanes will still be required to have a transponder on board. This is so the airliners, and business jets, will be able to see their traffic on TCAS. This defeats the purpose of ADS-B OUT traffic on your screen.
Another problem with the whole ADS-B system is it was devised on technology that is over 20 years old. ADS-B will be using ground stations instead of satellites. The FAA complains that it costs too much to maintain VOR’s and ILS’s because they are ground based. In my opinion it will cost as much or more to maintain the ADS-B ground stations.
ADS-B OUT will be required by 2020 in all controlled airspace. It is my understanding that as of today ATC is not able to see ADS-B OUT airplanes and still uses radar. As of today fewer that 5% of airplanes are equipped with ADS-B OUT. Today the minimum cost of ADS-B OUT to someone that does not have an IFR GPS in their plane is $4,000 for the equipment and approximately $3,000 for installation. This is a huge expense to the older GA fleet that amounts to approximately 15% of the value of one’s airplane with absolutely no benefits other than to see traffic. Embry Riddle University was a test for ADS-B OUT, and all their airplanes are ADS-B equipped. Being that Embry Riddle flies in the Phoenix area I am able to see traffic. ADS-B traffic is awakened by any plane flying in a 15 mile radius to where I am. It does not work if there is not an ADS-B OUT plane in my vicinity.
If the FAA truly believed in safety they would turn on all the ADS-B OUT stations 24/7 to provide traffic for all....but then this is the FAA we are talking about, and they stated this is not going to happen. We recently lost 2 flight school airplanes in a mid air north of Phoenix. If they were able to receive traffic then this might not of happened. As it was we lost 4 people due to this not being turned on.
In closing, there is only one benefit of having ADS-B Out and that is traffic. The cost does not justify the requirement.