Nitpick: it's different. Cmd+D splits the current buffer in two allowing to view two parts of the same output without scrolling, whereas in iTerm2 it splits into two distinct buffers, each with its own shell.

I arguably prefer the Terminal.app feature, when I have the other one with window management like with Window Magnet, which happens to handle any window, not just what's inside the terminal (in which case I'd simply use vim or tmux splits)