[bustedromo]

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A good poker player should consider an OOP river bet smaller than 1/4 * Potsize as zero information and do what he would do if it was checked to him.

If I were BB I would have raised to 1/3 or 12 * Potsize and fold to push of course. You don't save value by just calling in this spot, unless you have a super read on Hellmuth.

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I don't think it's this simple.

Let's say you have a marginal hand, think you're probably ahead, but you also have villain on a marginal hand, thinking he's probably behind, and if you check to him he thinks he must bluff 1/2 pot or better to take it down.

It's a marginal situation and above all you want to keep the pot size down, so you don't want to make a semi-bluff with your hand, and you don't want to put to a big decision on whether to call a substantial bet by villain. But you also don't want to give up your hand to a bluff.

You have villain on thinking that his chances of a successful bluff are marginal. Only if you check to him would he attempt the bluff.

In the above case, where the both your hand and the hand you put villain on are marginal, and your not really sure you're ahead, a blocking bet can really work to keep the pot size down. Just adding that little bit of extra doubt in villain's mind about the chances of his bluff succeeding can get him to opt in favor keeping the pot size small and just calling.