The idea behind sharding is to essentially parallelize the blockchain by splitting the one big chain into many smaller chains which can communicate with each ot

The idea behind sharding is to essentially parallelize the blockchain by splitting the one big chain into many smaller chains which can communicate with each other asynchronously. This is a really difficult problem for countless reasons but if they can get it working it offers a lot of very important benefits. It can process orders of magnitude more transactions than a conventional blockchain without the loss of decentralization seen in schemes using dPoS such as Steem, light clients get to be much lighter while still maintaining high security, and smart contracts which live on an individual shard and do not require cross shard communication are massively more efficient and can operate at a far lower cost than smart contracts currently can. The last issue is probably the most important for Ethereum specifically because currently most smart contracts simply cost too much to operate limiting their usefulness. Much lower operating costs greatly expands their realistic use cases. If you'd like a detailed writeup I'd recommend reading the Sharding FAQ https://github.com/ethereum/wiki/wiki/Sharding-FAQs https://github.com/ethereum/wiki/wiki/Sharding-FAQs