Crashing a pool so yours gets better hash rates maybe?
That's just it, though. You're not crashing the pool, you're only affecting the pool's luck stats and impacting everyone's payouts including your own. I don't understand why. Let's say that you are successful in your attack, then what? Are you hoping that miners get disgruntled and leave that pool? OK, so now you have to hope that the miners that left all join your own pool? Seems like a long shot, and a pretty lousy choice of methods to get miners onto your pool, especially since by its very definition you're losing revenue you would have made just mining properly.
Let's say that I have 1PH/s of mining equipment and that I have hacked my miner software to not submit block solutions. I would have to launch my own pool, and then spend all of my mining efforts trying to disrupt the other pools, all while advertising and trying to draw miners into my pool. I'm losing revenue the entire time because I'm withholding block solutions. I'm playing the odds that by causing enough disruption in the other pools, a ton of miners will leave those pools and join mine, at which point I'd fix my software and hash away properly. Are those odds really that good? I wouldn't think so. I would think the revenue lost during my "exploratory" mission would outweigh the gains I *might* make later on.
There are some legitimate and worthwhile reasons for performing a block withholding attack. Let's say that you have a substantial percentage of your net worth in bitcoins and a pool operator is approaching 50% of the net mining rate, threatening the value of your bitcoins. Might it not make sense for you (and others in a similar situation) to mine at the offending pool operator's site with your miners configured to do a block withholding attack? Until the pool's luck is adversely affected, you would still receive nearly the same payout you would otherwise receive, but at the same time you would be negatively impacting the luck of the offending pool which would lead other miner's to switch to a different pool once they noticed their earnings began to decline.