The main difference between working for a big company vs. a small company is that the roles tend to be explicitly defined and specialized at a big company. You don't need/get to wear as many hats as you will at a small company or a startup. Basically, instead of being a jack-of-all-trades / "full stack" developer, you might become an expert on one layer of a huge technology stack. This can be good, or bad, or mixed. There is more formal training and you can get deeper knowledge, but it's harder to get broad knowledge. It can be hard to change roles or try new things. Generally, I think learning "full stack" is preferable when you're young, and specializing might be better as you get a little older.