User blog comment:Furbearingbrick/No More Spinoffs: Desperate Struggle/@comment-1778317-20130122041548/@comment-5643552-20130123211543

Maybe if you had a character that was immensely powerful physically, but weak in terms of mental capacity/emotional maturity. That way you could explore the whole "invincibility" thing in more depth, touching upon negative aspects of the trait in a way that you couldn't with a Mary Sue, but in a different way from if you made the character invincible but physically weak. There's actually a variety of ways in which you could make invincibility an interesting character trait, it's just that most people prefer to use it to enhance their character's "awesomeness".