You can use it to make websites, do scientific computing, NLP, email processing, datamining, big data, etc. If you're just trying to throw up a website then Ruby or Javascript are fine, but if your backend involves lots of different types of computing then Python is pretty much your only option. So if you have an idea for a minimum viable product but you don't really know where you want to take it two or three years down the road, then it really just seems like the most pragmatic option.