Why do people buy speakers and headphones with a pc?

I've seen when people buy or build a pc, their setup usually has both headphones and speakers. What's the point of buying speakers when you have headphones? Or headphones when you have speakers? I'm asking because I plan to build a pc, but I don't know if I have to buy speakers although I have... show more I've seen when people buy or build a pc, their setup usually has both headphones and speakers. What's the point of buying speakers when you have headphones? Or headphones when you have speakers? I'm asking because I plan to build a pc, but I don't know if I have to buy speakers although I have headphones already.
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