There's some minor things that iTerm2 does that I like:
You can hold down command and click URLs to open them. (You can actually kinda do this in Terminal.app as well by right-clicking a URL and choosing to open it, but it's a bit fiddlier, and I got used to the hover feedback in iTerm2.)
You can click to highlight entire blocks of output from commands, which I sometimes find handy when things feel like they're blending together.
It'll keep a floating copy of the previous command prompt at the top of the screen so you can see what led to whatever output is currently at the top.
Though I don't know how to do the third, Terminal.app supports the first two. Command+double-click opens URLs, and you can select the content of the last command with Edit > Select Between Marks or shift-command-A. (Terminal.app automatically adds a mark each time it detects a new prompt, unless you turn that setting off in Edit > Marks.)
This is actually one of those cases where the ease of doing it makes a real difference to me… iTerm2 does both of those on a single click, and that makes it vastly more likely that I’ll use them. (Completely a matter of taste, I’ll admit.)
You can hold down command and click URLs to open them. (You can actually kinda do this in Terminal.app as well by right-clicking a URL and choosing to open it, but it's a bit fiddlier, and I got used to the hover feedback in iTerm2.)
You can click to highlight entire blocks of output from commands, which I sometimes find handy when things feel like they're blending together.
It'll keep a floating copy of the previous command prompt at the top of the screen so you can see what led to whatever output is currently at the top.
None of these are essential, for sure.