I thought about this a bit and it seems that having it connected to a single pool means that you want to bet on the pool's luck. Having it spread among 2 or more pools means to eliminate the luck factor a little bit. Of course that it works on both sides, if you have it spread and one of the pools is extremely lucky, you just lost a bunch of BTCs.
If you mine longer than a few weeks (you'll have to do that for months to ever break even ;-), it all evens out. That is the nature of luck