There is quite a bit you can do on Android that you can't on iOS, way too much to explain here. Some people make use of it, while others don't. Just for the basics, how about arranging the icons on the homescreen the way you want without being forced to start at the top and have them fill up from top to bottom and left to right? What if I want my icons on the bottom instead? What if I want a widget with the time and temp on the main screen but nothing else? Then you can change the themes of the entire OS. Want a dark theme? Sure. Want a purple theme? Here you go. Android is all about customization.
For multi-tasking, my example is a bit of a geeky reason but here it is. I load up Google Maps to navigate while streaming music, but at the same time I have Sensorly running to map the coverage for my carrier, and have WigleWiFi also running to map wireless networks. I may load up SignalCheck pro as the front screen app so I can see what LTE band and signal strength I have. Meanwhile, Google Maps will pop up over the top of my screen giving me directions for my next turn.
I completely agree, if you need more storage than what the base model offers it's a hassle. For me, I like it because the base model was 32GB compared to 16GB on the iPhone, and throwing in an SD card let me have a buffer if I temporarily needed more space, like loading videos for a flight.