It doesn't need to be accidental, miners may deliberately choose to *partition* mempool like in **a kind of** sharding. Suppose people divide mempool space to odd and even transactions and miners randomly or deliberately choose to include each shard. Now the discovery of an odd block won't invalidate the even blocks under process.

What would be the benefit ?

For the rare cases where two miner find a block at 'the same time' ?

What stops me to create a 'parallel' block to the second block created then ?

I'd get 50 BTC reward, right ? Since it is height 2.

And if, in your theory, that's not possible because the height would be the (real) height (in terms of block order), then you would have a normal blockchain imagining the chain to bend 90°.

With referencing to the previous block, that's then just an illustration. But nothing would change.

What if both parallel chains get a parallel chain? What if the parallel chains of the parallel chains get parallel chains? You might end up with 4 chains, then 8, 16, 32, 64 (offcourse, not all parallel chains have to get parallel chains at the same time, but i hope you see my point).

That's (Block-)

**chainception**.