I joined because of the heat map. I tried to post all my in-town rides with the hope of making the city planners aware that hey, people ride bikes in this city.
I went premium because my wife wanted to have some way to know about where I was on the bike, so the live tracker feature kept me in.
Of course RWGPS has a tracker now, plus better navigation tools and a broader base of rides. So I'm not giving much up to stop paying for Strava.
As always, YMMV.