[hylaride]

You can save layouts (when I start iterm, it loads multiple windows on different monitors with split panes and tabs the way I like them).

More advanced search with regex support, more advanced paste (can do character encoding transformations, deal with special characters, etc), smarter and configurable text selection, autocomplete (mixed bag, TBH - I use zsh for that), more advanced snippets for repetitive commands, and triggers to notify you when things happen (long running commands finish, certain words pop up eg "error" or "compile done").

It has a basic integrated password manager that allows me to paste passwords I commonly use in the terminal with a keycombo.

It can more tightly integrate with the shell/program. You can select a point with the mouse in vim or the shell and the text cursor will go there, for example.

Some of these may have since poked their way into the built in terminal, but these are some of the main reasons I use iterm. If you spend a lot of time in the terminal, you can enhance your productivity.