Can someone explain to me why after being vaccinated, people should still distance and wear a mask? Is it for social signaling or is it for medical reasons?

OK, follow-up question – some people are saying that it may still be possible to spread the virus if you have had the vaccine, which I get. What’s the normal run of these things? Like, when does the data get clearer about whether it’s possible to spread it if you’re vaccinated?

Thank you everybody for your answers in the links! I’ll read up. I’m nowhere near getting a vaccine anytime soon, just trying to understand where the science is in this right now.