Larger pools almost guarantee income if you mine proportional. Smaller pools are a massive gamble, you may not even get paid at all
if the pool is at ~30-50ghash and fails to find a block for a month & everyone bails out of a sinking ship.

Point in case: btcpool24.com, completely died after encountering multiple 95+ percentile rounds at low speeds.
Over 5 million shares went to waste for nothing on the 'death round'. Miners bore the brunt of the losses, not the owner.