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.
Yes, beware of this. It seems many of the small pools have no plan of action for when their pool dies. In many cases, submitting a share is gambling that the pool will last sufficiently long. For bigger pools or PPS pools this is not an issue.