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I do both, and it's not the same thing. When your voting power decreases (mine's currently at 56%) the amount your vote gives out goes down. Giving a tip is a direct donation from you, not from the rewards pool.

But dont it all came out of the pool in the first place?

They do, but so does USD from a federal mint. If you get a dollar from me or a dollar printed by the mint, there's certainly a difference there. The FED doesn't just give out free money though. At least, it doesn't give it out to regular people like you or me, just banksters and governments.