Mark (at one of his first Rebreather-Dives) and Dolphin
In my eyes the main advantage is in nature-observation.
Rebreathers are extremely quiet, compared with open systems, this is the reason why more wild animals will come and observe you.
You also have more time for observation:
Then you need 100bar*l/min Air in 30m on OC, on CCR you only need 1bar*l Oxygen per minute, independent of depth.
Also your Decompression is optimised on CCR: on OC-Air your no-decompression-time on 30m is about 15minutes, on Nitrox-CCR you can stay 31minutes at that depth without the need of decompression-stops (calculated with ppO2=1.6bar and "Deco92-II").
Diving with rebreathers is no novelty, it is the original way of SCUBA-Diving and possible since about 1879.
http://Rebreather.de/rebreather/advantages.htm © Karl Kramer, 28.8.1998