GrumpyOldGuy
Contributor
Check out Chapter 6, page 82, paragraph 3 of the SDI manual. Your answer is there with the reasons - don't need it, it's an extra failure point, it creates extra drag. I'll add one of my own - if you do happen to be diving with a buddy who goes OOA it's confusing to have three options for him to grab.
I moved my octo from my 1st stage, got a bright yellow hose and octo holder and put it right where it would be expected. I discuss & practice deployment with any buddy I happen to dive with before the dive. Pony is always on/valve open so nothing to do but grab and breathe. My primary 2nd stage hose is way too short to give up. We would be nose to nose plus I can hand off the pony and we can ascend together but not tethered.
Just to be a PITA,
1) Although it is an additional failure point, since it is run in parallel this is mitigated depending on the failure mode.
2) The extra drag is so small as to be unmeasurable, its a non-issue.
3) Proper procedure is YOU offer your 2nd to the LOG/OOG buddy after he signals, no reason for confusion with a trained buddy.
4) If the OOG buddy is in full panic or newbie, he will just grab what he sees first, he won't have time to be confused.
I am back to there is not a compelling reason you must use either method, both work.