The Usefulness and Reuse of Masks

Early on in the pandemic, I think I was informed that masks would insulate the wearer from the world, particularly the viral particles floating around in the air from those already infected.  So it made sense that masks were one-time use--you go out wearing a mask, you meet someone infected and his virus particles get hung up in your mask. You then go home, and the mask represents a threat to anyone who contacts it.  Fine.

But now I'm getting the impression the main function of the mask is to protect the world from you, the wearer.  It captures your germs, your viral particles.  Is that true?  If it is, then the mask can be used more than once.  If you're infected, and the mask captures your virus, there's no new contamination in the home and no real downside to reusing it.