Well, you don't really _need_ to; this one is just syntactic sugar, and the others, while nice (or mostly; I'm unconvinced about ARC), are not necessary. I'd prefer to have the options.
ARC is not really 'needed' for anything, it's just a very nice way to prevent memory leaks and pruning lots of retain/release statements from your code.
I would not re-factor existing code without ARC if it was properly debugged for memory leaks and working perfectly, but for all new projects I have it enabled.
Well, you don't really _need_ to; this one is just syntactic sugar, and the others, while nice (or mostly; I'm unconvinced about ARC), are not necessary. I'd prefer to have the options.