I went out to buy a pony bottle and realized that it was a marketing gimmick and I don't need to spend money on it, so I went home. I then read that it is good to be self reliant and a simple pony bottle accomplishes this
So I went and purchased a pony.
I hooked up my pony to go diving when i then found out that in an OOG situation with my buddy takes 9 minutes to surface from 90 feet. I must be dreaming as my little pony...isn't gonna cut it for me and my buddy. So I put it back.
Then I thought what the hell am I going to be doing to waste 9 minutes doing in an OOG situation. So I grabbed my pony.
I went to go dive with my pony then was told I must not be planning my dives correctly and if I was that I should never need a backup for my air in emergency situations beyond my buddy. So I put the bottle back in the car.
I then realized that no matter my gas management skills that emergency air situations can happen for numerous reasons and my buddy might not be close enough or able to cope. So once again I grabbed the bottle.
Then while gearing up my buddy noticed the pony and assumed that it must mean I'm a bad buddy and plan on losing them, so put it back to help them feel comfortable.
Later, I pulled the pony bottle back out so I'd always have my own backup because really you never know when even a buddy might not work out and it shouldn't matter if they are insecure about it or if they simply decide to ditch me to join another buddy team.
Then I put it back after the coming to the conclusion that i must want a pony because of my own insecurities of the buddy system and that I am the bad buddy and along with gas planning, I and should work on my buddy skills.
A bit later I pulled the pony bottle out again with the rational that Its always better off having backup air in any scenario, especially if I'm a bad buddy. I shortly after realized my mistake and now see I should have gone with doubles and put the pony back on the shelf.
I finally then grabbed the pony bottle and realized I should use it if it is what I want to use and will continue to second guess my choices as I read others opinions. Thank god for scubaboard!
As far as I know the only backup commonly used for belaying is for braking and many still do not use those.