Killer feature for me is being able to cmd+click on file paths in the terminal to open them. I use this constantly. There are plenty of other features too such as being able to reopen a tab you closed accidentally.
And that tab will have the same shell environment?
>open file paths
That is convenient if you get lots of paths in terminal, maybe "svn stat" is a good example. Btw, cwd may be opened via "open ."
For a while it had a lot of features that Terminal.app was missing. Terminal.app has fixed a bunch of these things, but iTerm is still my preferred terminal app on macOS. iTerm has overflowing with features (though that doesn't necessarily mean that they are useful to you).
What doesn't Terminal.app have that iTerm has? Asking because I'm heavy user of the terminal on osx, and wonder what you're really missing there.