If they want to do it every 3 blocks, they might want to make sure the transactions won't have trouble getting through in case 3 blocks are mined rather quickly after each other. Or, they just had 300 BTC handy that they didn't want to split up. Or.... ??
If I sat there using online banking to transfer money from one account to another over and over - my bank would put a hold on my account. I think there should be a way to prevent this. This one person is unlikely to have any effect but if the bot-net dickheads get hold of it...