"Lowers Nitrogen absorption and (therefore) reduces the chance of DCS" - I do not agree with either one of those statements. If that is what Nitrox instructors are teaching these days, then it is clear to me that they do not really understand Nitrox.
It is true that diving to equivalent depths and times on Nitrox will result in less Nitrogen absorption than the same depths and times on Air. If that is what people were doing, then I would grant that the above statements might be true. In my experience however, that is not how most people are using Nitrox. The most common use of Nitrox (and the purpose for which it was developed) is to extend bottom time at a given depth, or to go to a deeper depth for the same amount of time. If a person dives to the limit on Nitrox, then they will absorb just as much Nitrogen as if they dived to the equivalent limit on Air. So from a practical standpoint, I don't see "lowers Nitrogen absorption" as a tangible benefit, given how Nitrox is typically being used.
With respect to DCS, the operational aspects of the dive have much more to do with increased risk than the breathing gas does. Divers who ascend too quickly or hold their breath while on Nitrox, will be injured just as surely as if they had done the same thing on Air. There may be some marginal reduction in the chances of DCS, due to "slower effective ascent rate", or to breathing higher PPO2 at the safety stop, but I am not aware of any studies that support this notion. So again, I see no tangible benefit to using Nitrox for the sole purpose of "reducing DCS risk".
Nitrox is not some panacea that will automatically reduce risk of a diving injury. As divers, we all have the responsibility to follow safe diving practices, and the standard safety recommendations always apply, independent of the breathing gas - do not push the limits of your table or computer, always ascend slowly, and do safety stops on every dive. These things will reduce the overall risk much more so than the choice of breathing gas.
To answer the question that Kamala posed, I see the primary benefit of Nitrox as extending bottom time, for divers who have good enough air consumption to take advantage of it. And I guess I see some benefit to diving Nitrox on Air profiles where certain risk factors may be present (cold , etc). There is also some anecdotal evidence to suggest that divers "feel better" after Nitrox dives than after Air dives, probably due to reduced partial pressures of Nitrogen during the dives (my own experience diving with Nitrox bears this out).
But I don't really see "lowers Nitrogen absorption and (therefore) reduces the chance of DCS" as being applicable to most Nitrox dives, insofar as how most divers are conducting them.
(Sorry if I came on too strong with this post - this is a hot button topic for me, and I guess I get kind of crabby when I see people referencing these particular "sound bytes".)
-JimG
Well, I guess it depends on your air consumption relative to your Nitrogen limits. As someone who is more of a heavy breather, I seldome hit my NDL. So I do believe in my case, it does reduce my absorption. Where I do get the benefit above is in multi-day diving, where I don't have the long term buildup of Nitrogen in my system the further reduces my bottom time.
