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I realize this question may not have an answer and therefore might not be suitable for SE, but I'm very curious about OP_RETURN transactions.
OP_RETURN transactions appear to be the accepted mechanism for inserting metadata into the Blockchain. Considering the innumerable uses for metadata (contracts, colored coins, proof of ownership...), I foresee more and more non-monetary transactions filling up the Blockchain.
Will that be bad?
Why is "growing the number of unspent outputs" a "problem"? – tim peterson – 2014-08-31T16:26:24.317
1@tim peterson: Client software needs to keep track of unspent outputs to be able to verify future transactions, so unspent transactions require storage space. It does not need to keep track of transactions that have already been spent; once it has used them to verify the following transactions, they could be discarded (though some clients like Bitcoin Core keep them around anyway). – Nate Eldredge – 2014-08-31T19:03:52.097