Lol, compumine with tree chains you only need the history of the coins you own so no need to download huge 40GB blockchains like BTC, this would be great for mobile devices.
Also rather than everyone mining the same block at once (big companies with big hashing power wins) lots of different parts of the tree can be worked on by everyone so no centralised mining either yay

sidechains are a way to transfer $100 from LTC blockchain to BTC blockchain, like an extra layer of software in the middle that keeps track of everyone doing this so there is no double spending and no coins are lost but all these blockchains will still be growing and mining will still become more centralised

This is my understanding compressed into few sentences