I'm a sucker for schlocky sci-fi movies with lots of special effects and CGI (computer-generated imagery). But I didn't realize until seeing this just how many "ordinary" movies and TV shows employ CGI effects:
Even if you're not making a "special-effects" movie, it's apparently a lot cheaper to set up a green-screen and composite in a shot of Paris than it is to go on location. I also learned from this Quora discussion (with contributions from seveal film-industry experts) that most shots of ocean these days are computer-generated: it's easier to simulate the surface and waves than it is to deal with weather, camera movement, etc.
Quora: What are things in movies you don't expect to be CGI, but that typically are? (via Jeremy Howard)