Merged mining is used by certain cryptocurrency miners when they start mining two or more cryptocurrencies at the same time. They try to do this one the same mining machine and try not to be sacrificing overall mining performance. 

You can do this too if you’re a miner by using your computational power to mine blocks on multiple chains at the same time. You’ll just need to learn how to set up Auxiliary Proof of Work (AuxPoW).

When you use AuxPoW your mining machine can leverage valid work on two different blockchains. You’ll want to set the blockchain that provides the proof of work as the parent blockchain and the other one that accepts it as valid will be set to be the auxiliary blockchain.

Just keep in mind that for this to work, the cryptocurrencies you mine must be using the same algorithm for their proof of work.

As an example, Bitcoin uses SHA-256 in securing its blockchain. This means that almost any other coin using SHA-256 you can set to mine along with Bitcoin.

The benefit is that the parent blockchain is not affected that much and doesn’t have to go under any kind of technical modification on your part. The auxiliary blockchain may need to be programmed for receiving and accepting the work done by the main parent chain. 

Smaller coins and blockchains may want to implement merged mining because such small (low-hash) blockchains thereby increase their security when they go about leveraging the hashing power of Bitcoin or another bigger chain such as Ethereum. This increased security prevents 51% attacks -- though enough miners need to agree to adopt merged mining.

Nevertheless, some debate whether merged mining provides a false sense of security. This argument stands because a relatively big mining pool could still reach 51% hashing power on the smaller chain and make that attack possible. Still, if the reward or incentive is good enough to mine this auxiliary chain then more miners will join and thus keep reducing centralization and increasing security. 

Then again, what if the merged mining removes economic losses from the process because, as an example with our Bitcoin miners, they  can use their hashing power on the smaller chain and not risk their Bitcoin block rewards. This means that these miners wouldn’t be as inclined to act honestly on the smaller auxiliary chain.

In the end, if you’re planning on investigating this method, please do your research deeply and set up your equipment correctly.