https://github.com/monero-project/monero/pull/1753 is a pull request for disposable addresses and sub-addresses but what is a sub-address? Kind of like bip32 wallets in bitcoin?
There are disposable addresses and subaddresses. Subaddresses are cool because you can have different addresses and still have them go to the same wallet. But they wouldn't be linked together.
As pebx mentioned, there is a limit on the amount of subaddresses. You can generate as many subaddresses as you want, but the wallet cache file size gets bigger and bigger as you generate more because all subaddresses need to be stored in the file. For example, 10000 subaddresses (the default setting) consume 400kb, and 100k subaddresses consume 4MB.
That's where the disposable addresses come in. Because you could say "what's the point of a disposable address, I'll just create a subaddress every time!" which would be fine in theory but
since there is a limit, it makes more sense to use a disposable. Especially when you are only using it for one transaction.
At least that is how I understood it.
I will quote some comments from kenshi84 (who submitted the pull request).
Subaddresses are just like the standard address that you can use for receiving funds repeatedly. For example, you can use subaddress of index=1 for receiving your salary and index=2 for raising funds for your secret project, and no one can find the link between them.
The number of subaddresses that you can generate for your wallet is limited due to storage requirement (currently the limit is 10000 addresses and they are precomputed during wallet generation).
The number of the precomputed subaddresses is set to 10000 by default, and can be changed via