What are the trade-offs between using a monorepo and a polyrepo in frontend system design?

Imagine you have a big box of toys (monorepo) where you can easily find and play with any toy, but you need to keep it organized. Or, you have separate smaller boxes (polyrepo) for different toys, which makes it easier to find a specific type of toy, but you might need to open many boxes to play with them all together.