Quote from: ACVentures on November 21, 2013, 06:09:20 PM

I was under the impression sweeping would move the coins off-chain without incurring any possible transaction fee, and would do this instantly without need for confirmations. The more I think about it, the dumber that sounds as the rest of the network would have no idea those coins were "moved" in the first place.

I'm now a bit confused as to why someone would wish to sweep coins at all. It seems you need to have total control over both wallets in either scenario. You're also advising to never "delete" a wallet. If sweeping still means the coins get sent as a transaction to a new address, how is this different than a normal send?

In my question I do not care at all about signing messages or proving ownership at a later date. I'm more interested in keeping funds secure and organized. I also do not care about the astronomically remote chance of a private key collision.

So, the million dollar question: Why sweep at all, ever? Would the best course of action to be keeping all of the older wallets empty after draining them with a single transaction to the armory wallet, which would consolidate everything?

It is only recommended you use "Import" when you are sure you're the only person who's ever seen the private key, and you plan to use it again. Since address re-use is discouraged, the only real reason would be for vanitygen addresses which are frequently used without. Otherwise, always sweep, especially for Casascius coins and paper wallets which have been passed around.

WHy? Because it's extremely dangerous to add private keys to your wallet that other people have seen. You open yourself up to situations where someone "sends you money" by sending it to the address that they have the private key for. It shows up in your wallet and looks like it's yours. You act on the assumption that the money is yours, then they sweep it back to their own address. This is a major attack vector against someone who accepts large amounts of money for services. You pay, they serve, you sweep, they're screwed.

And don't fall for the argument that "all keys should be held on forever in case someone sends more money to it." Someone randomly sending money to a private key that has become public is like dumping money on the ground. Any actions you take to "watch that address" is like walking around your neighborhood every day hoping someone accidentally dropped $1 bill. One day you might get lucky and find $1, but you have better things to do with your time, and it's best not to pollute your wallets with mixed-origin private keys.

You want to know that when you receive money to any of your wallets, it's really yours. If there's no reason to believe the key will ever be used again, sweep it.