Most so called 0% pools are actually taking some of the mining returns, be it transaction fees, merged mining or both.
The rest are doing some kind of loss leader, either to promote another product, to build their brand, or to build a the personal brand of the operator.
0% fee does not necessarily mean a pool is a good pool to use or that it is a bad pool to use. Don't be hypnotized by that number. It is powerful.
eh, what could a scrypt p2pool 0% fee, 0% donation take?
(The altcoin forum is
that way.)
I don't really follow scrypt coins; is there such a thing as merged mining? If not then they're just running a loss leader promoting another product or brand.
Neither a loss leader nor promoting another product or brand means they are doing something intelligent. Might be an ineffective strategy.
They might be skimming (harder in the case of p2pool but not impossible if they are running the node, though they probably get caught at some point, if they're not gone first), but really this could be true of pools with a fee too. Greed is greed.