It was mentioned that Batman’s cape has a purpose, which is awesome. There’s another hero who’s cape has a purpose other than just being there though, Spawn. His suit is sentient and connected to his nervous system, and he can manipulate the suit to benefit from various abilities like shapeshifting, attacking or deflecting attacks. The cape comes into play many times when he’s fighting, it can stretch and tie people up, he can disappear in it and quickly travel to some other location, stuff like that.
But since the suit itself is a major part of his powers, and is alive, is it really a standard suit and cape? But it definitely has its uses, and is not just there for show.