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If you start making alt accounts, you may want to set your main account to be able to recover them. Also, if you are giving accounts to family and friends who may not be as savvy. Or for example, Steemit now wants a telephone number and an email address, maybe you don't want to give that personal information to Steemit. Finally, it would be pretty crazy if steemit had this monopoly.

My account is set to Steem as recovery, even though I used Steemit to sign up. I don't know what happens if you use another large dapp. I have a few extra accounts, and I would happily give them away to anyone kind enough to ask and I don't even want anyone's phone number or email.