Manual withdrawal only costs 10k satoshi, so for withdrawals > 0.02 BTC, its cheaper to do them manually since at that point 0.5% of the sum becomes more expensive.
Auto cash out doesn't cost 0.5%. It's actually completely free.
So auto cash out is always cheapest. But you may want to cash out before reaching the minimum for the auto cash out, or you may want to send less than your entire balance somewhere - in those cases the manual "send coins" is useful.
Whoa, wait Doc - it
is free! Am I losing my memory or did it "cost" a 0.5% donation at one point?
And actually...now that I think of it, do mining pools qualify for status as non-profit organizations? Because logically, if the IRS wants to tax mining income at the income rate - donations to the pool should be equivalently tax-deductible for miners.