I just had a new thought on dive buddies and particularly insta-buddies. You may recall I previously said: "I am responsible for my own safety and as to my safety, a buddy is just a potential asset." And, "I'll take whomever the DM assigns. If it shortens my dive, that is just a risk that comes with not bringing my own buddy."
I was just thinking: A dive buddy is like an essential piece of equipment. If you don't bring it with, you may end up sitting out the dive. If someone has a spare, you may be able to do your dive. It may not be perfect, but at least you may be able to do the dive.
Say, for example, you forget or break your tank. Unless someone has a spare, you will end up sitting out the dive. However, if someone has an extra tank, albeit a small one, you will be able to do the dive. You may not be able to go as deep or stay down as long, but at least you will be able to do the dive.
An insta-buddy is like the borrowed tank. You may not be able to go as deep or stay down as long, but at least you will be able to do the dive.