What's the point for mining pools to set a higher target?

Question

I'm reading the Mastering Bitcoin 10th chapter, and quote

Similarly, a mining pool will set a (higher and easier) pool target that will ensure that an individual pool miner can find block header hashes that are equal to or less than the pool target often, earning shares. Every now and then, one of these attempts will produce a block header hash that is equal to or less than the Bitcoin network target, making it a valid block and the whole pool wins.

1. I'm wondering what's the point to set a higher target value? If the pool ask the miners to search the same space wider than the Bitcoin network target, some of the miners' work are wasted for sure.
2. How does the mining pool split the work?

Answer 1

I think the quote is perhaps a little confusing. Higher target means lower difficulty (easier). Mining requires finding a block which hashes to a value lower than the target, so raising the target makes the job easier, because the search space is bigger.

With a higher target, most shares found by the pool participants will not be valid blocks on the actual bitcoin network. They are just a way of tracking the relative work each participant in the pool is doing, so that the reward can be split fairly (based on the proportion of shares each participant submitted).

However, while searching for shares, some will also be valid bitcoin blocks. These are then submitted to the network and the entire pool is rewarded accordingly. It doesn't take any extra searching to look for both at once (shares and valid blocks), because all valid blocks are also valid shares, by definition.

For more information about mining pool shares, please see: What is a share? Can I find it while mining solo, or only when pool mining?