One of the feature I like is time clocking[2] where in you time all everything that you do (including sleep![3]) and eventually review after a week/month/year, you can generate some analysis on what task took most of your time.
org-drill[4] helped me a lot when there are things that I need to memorize.
I used vim for one year before moving to emacs. Indeed, I can edit files faster in vim rather than emacs but I can get more stuffs than in emacs rather than vim because of org-mode. Therefore, I choose emacs for the reason that org-mode helps me organize everything.
[0] http://doc.norang.ca/org-mode.html
[1] http://doc.norang.ca/org-mode.org
[2] http://doc.norang.ca/org-mode.html#Clocking
[3] http://sachachua.com/blog/2015/11/weekly-review-week-ending-...