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I have previously asked questions and read about the importance of always using a new address every-time you receive a transaction, even for change. Sometimes when I watch the block explorer I see transactions where the send address and change address are the same, like this one:

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Tx: 7c99440257f45b2b87f655744a8ec4f87c73f54ca5a9873e083eae5214d51aa2

It is also my understanding that most wallet software automatically generates a new address for change. This leads me to believe that the transactions where the change address is the same might be people using more advanced wallet software that gives them more control over these features. Are there known reasons or types of users who intentionally choose not to follow the advice to use new change addresses?

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    I think that poorly implemented wallet software is going to be the reason 'why', in almost every case. – chytrik Mar 14 at 10:52
  • One can do whatever they please as long as it conforms with the consensus rules of the network. To that end, we can only speculate why some users choose to increase their risk and decrease their privacy. – m1xolyd1an Mar 14 at 15:21
  • Thanks @chytrik – Prince M Mar 14 at 15:24
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    Both things mentioned in the comments are true: 1. Poorly implemented wallet software. This also happens when you try to use Bitcoin as account based system even though each transaction with same change address used again will create a new UTXO to be spent later. 2. Freedom to create transactions in different ways as long as they follow consensus rules. – Prayank Mar 15 at 21:47
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    3. Speculation: Maybe the user doesn't care about trade-offs involved in using input as change and this setup works better for user. The tx shared in question has similar linked txs later, each using input as change and one output went to Coinbase exchange: i.imgur.com/g9wjpYm.png 4. Privacy: Things that a person doesn't want to share with everyone. Maybe this person is okay and aware of things involved. Sometimes using new change address also is easier to associate with same user. – Prayank Mar 15 at 21:59
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Are there known reasons or types of users who intentionally choose not to follow the advice to use new change addresses?

Say you perform a lot of transactions but still want to have some mechanism for your heirs to get to your bitcoin should you die. And say that you don't do anything you have any need to keep secret. In this case, it makes a lot of sense to re-use the same few addresses, the ones that you've made arrangements for your family to be able to access should something unfortunate happen to you.

The same logic might apply to a transaction system using an HSM with limited storage to secure the keys. Large numbers of addresses would mean large number of keys, meaning they couldn't all be secured by the HSM, reducing your security.

I notice you just reference "the importance of always using a new address every-time you receive a transaction, even for change". I have no idea what that importance might be, but so far as I know, bitcoin is perfectly secure even if you always reuse the very same address.

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    I'd also add, "say you want your wallet to be publicly auditable". If you, for example, are the treasurer for your local bitcoin investment club, by using a single address for all transfers, all of your members can independently keep track of all flows and how much money is left in the pool. – bigjosh Mar 18 at 18:55

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