Here’s the thing. If you ever need to use your alternate air source, it is very unlikely that you’ll be the one breathing from it. To review, the procedure for providing an octopus second stage regulator to your buddy is as follows:
1) Your buddy signals “out of air, share air.”
2) You make the octopus accessible for your buddy to remove from some kind of quick-release mechanism holding it within the triangle formed from your lower rib cage to your chin.
Forget about the damage to reef systems, and sand and other debris getting into the alternate air source. Your buddy has been trained to expect that regulator to be in that location, and if it’s not, expect to be fighting over your primary–or worse.
If your buddy does manage to get a hold of your primary regulator, don’t expect to get it back. You’ll very likely find yourself scrambling for the alternate, which could be anywhere.
The bottom line is that it is a critical piece of safety equipment that you’ll probably never use except in training. Don’t neglect it. On the outside chance that you do need it, the consequences could be tragic.