The bragging thread encourages a focus on personal accomplishments and personal improvement. It becomes easy to assume that the only things of worth are self-focused actions. Not a bad thing when you want to focus on self-improvement, but it does not demonstrate any connection with saving the world at large. A "Saving the World" thread encourages considering large scale actions and effects.

At least this is my opinion. As Christian said, we would just have to see what the reception is. Might be unnecessary, might be helpful.