Quote from: frha on June 24, 2016, 11:24:29 PM

I notice that every once in a while, there comes along blocks with lots of space left over even when there are loads of unconfirmed transactions.
Like this one : https://blockchain.info/block/000000000000000004ae1a3b7ac7c7422a779e4ea9eb8e3c14935a80ca51dc17
This block was mined when there was over 6000 unconfirmed transactions.
What's the logic behind not filling up the block? Don't this just delay the whole network and give less transaction-fees to the miner ?

There isn't really an logic to it. It may simply be that the miner's node is set to a point where many of those unconfirmed transactions are rejected. Additionally, there are many many empty blocks that are mined. IIRC if all blocks had the same number of transactions, there would be no backlog and no blocks would ever be full. One of the easiest ways to increase capacity is to have miners not produce empty blocks.