It's not on by default, because it's not the default when using git from the command line. If someone is new to git it might be a little scary to see a wall of text when committing.
I'm not sure that it's actually documented though, which definitely is an error on my part.
You can actually stage and unstage hunks from a diff view. With a diff view open, you can press + or - to increase or decrease hunk size, n/p and N/P for next/previous hunk/file, and s/u for stage and unstage.
I'd probably say the status view (ala magit). Last time I tried kemayo's plugin it was all happening in ST's quick bars. However, that was a year ago so things might have changed.
Also, I try my best to keep up with user requests, which leads to about 1-2 releases a month. While there are occasionally bugfixes going into kemayo's plugin, I'm not sure if it's receiving any significant development (not trying to call anyone out here, it's just my observation from occasionally looking at the repo).
I've got an outstanding issue on that. Will probably be fixed within a couple of weeks. I'm hoping to do it in a somewhat backwards compatible way, which makes it a little difficult.
This has committing, staging, pushing, pulling etc. Actually, a lot of people seem to be using this alongside GitGutter, since their functionality is very much complimentary. See this issue for instance: https://github.com/SublimeGit/SublimeGit/issues/27
It is a little bit of a weird bastard child of the ideas in magit and fugitive, coming from vim and fugitive myself, but having always admired the workflow of magit. Mix that with whatever is possible interface-wise in Sublime Text, and you have SublimeGit.
I think it depends a lot on your workflow. If you're comfortable with, and used to, the command line this might not be for you. But for easy staging and committing of individual files/hunks I find it very useful. Also, even if you're just using Sublime Text as your commit message editor, this will give you color highlighting of you commit message, including gently nudging you towards good practices for commit messages.
You can actually turn on verbose commit messages by using the setting git_commit_verbose. Have a look in the default config for SublimeGit. If you do that, it'll add the diff, and even syntax highlight it for you.
I know... It's been on the todo list forever. Hopefully I'll get around to it soon. But to be honest, I'd much rather spend the time adding features to SublimeGit itself.
I hope that for 10€ most people will find it worth it. If you've already spent 60$ or more on Sublime Text and upgrades, I can see why this might seem weird. However, as the homepage says you can basically install it and use it for free as long as you like. You'll get a popup occasionally (if you do use it), but that's the only "restriction".
Also, for a free alternative, I have to mention https://github.com/kemayo/sublime-text-git which inspired SublimeGit. There are way more people using this, and it's been around forever. Personally I like mine better of course, but I realize that different people need different things :-)
Not at the moment, since I don't use mercurial myself. If there isn't a good mercurial plugin, then maybe that's for someone to look into? Writing a plugin for Sublime Text is quite pleasant (it's done in python).
Wow... So yeah, I made this. Woke up this morning to a slew of twitter mentions and quite a few orders. Thank you so much for the support!
I'm about to get on a 14 hour international flight in a couple of hours, but i'll be happy to answer any questions. Also, i'm tweeting from @SublimeGit every once in a while.
I'm not sure that it's actually documented though, which definitely is an error on my part.