An example: suppose you have some distributed system storing article metadata and all of the sudden one of your articles becomes very widely shared. The machine that the popular key hashes to gets slammed. Perhaps we'd want to adjust it so that that particular machine is just dedicated to that one article, or some other way to distribute that one article across multiple machines. But we're just using a hash function, so without doing something fancier, we can run into problems when the load suddenly becomes wildly uneven.
Your typical Kademlia DHT has k-replicas of each piece of data, so you read near the target node (node closest to the target key) rather than directly from it. This way, nodes at different points in the network read from many different replicas.
Of course, this depends on your consistency requirements.