I've learned a massive about the world in the process - before I started playing I wouldn't have had a proper image in my head for what certain parts of the world were like really. And there's lots of weird and curious things you learn along the way - it's an interesting mix of so many different things.
And it's just fun which is the main reason for playing. I probably spend about half an hour a day playing and I don't intentionally spend time learning stuff like car meta - I try and mostly go on what places actually look like. I have learned a few things that are fairly useless but nothing that has been too arduous to learn, and e.g. when I was learning the names of provinces of different countries, I was trying to learn stuff about the province at the same time so I know something about the culture, food etc. too.