Last time SpaceX tried to land its reusable rocket - the first stage booster and fuel tank of the Falcon 9 - it missed the platform by a hair's breath. It didn't even explode this time - it just flipped over. Unfortunately, the damage caused the rocket to be beyond repair, and hence far from being reusable.
There's a lot at stake here. Once SpaceX masters reusable rockets, well... a whole new era of space exploration might be rapidly ushered. For one, Musk estimates launching meat (astronauts) or cargo would be 100 times cheaper than today. This could transform our planet for the better, and fast. While not everybody might be able to fly in space, a lot more people will. Launching on the cheap means that deploying a swarm of satellites that serve free internet anywhere on the planet is feasible. On the long run, it also frees up an immense amount of resources for more important missions: building a colony on Mars (something that Musk is heavily emotionally involved in) and landing astronauts on asteroids. This isn't a pipeline dream. All of these could happen in the next couple of decades.
If, that is, SpaceX can manage to land that damn rocket safely on a platform in the middle of the ocean. Do think it's that easy? Well, try it out yourself and you tell me. Personally, I have finally come close to the level of agony SpaceX engineers went through in their past launches. The only difference is I actually failed 147 times; yeah that and, well, one tiny detail: this is only an 8 bit video game. Whatever. I couldn't land the drone ship once! Rage quit all the way...
Thanks to Verge for the tip.