Idle speed

Hi, just a question about idle speed. Is it bad setting the idle speed lower than factory specs? Mine sounds and runs much calmer at 7-800 than the 900 it's supposed to do but was just wondering if it does any harm? The only thing I could think of would be oil pressure but even at 600 where it still runs smooth it fine. Any comments?

It's an auto. I've been doing this for years without problems even during the winter. Even the power steering at idle doesn't kill it. Or even slow it down.

I am sure having it lower will do not harm as long as the alternator is doing its job.

Cool, I've got a voltmeter installed and it seems fine even with load. I wonder what the prescribed idle speed is actually based on? Thanks!