this is a winner take all pool. the size of the it has no meaning to an individual miner.
for sake of argument pool is 2ph or a block a day with normal luck. it is made up of 1200 sp20's . when one of them hits that block it is theirs alone. since the pool hits a block a day with normal luck the chance of your sp20 would be about 1200 to 1 your payout would be 24.875 btc . the rest goes to CK.
If you solo mine by yourself in your home with that 1 sp20 your chance is still 1200 to one. the advantage to using CK's pool is no maintenance of a server to run the blockchain to mine on it.
Every 'small' miner should toss some gear here not a lot but some. I run 1 defective s-3 here with ⅓ of the hash the other ⅔ goes to Btcguild.
I have I guess 99gh mining here. the s-3 has 2 dead chips send 99gh here and 260gh to btcguild
so my little 99gh has a 1 in 20,000 chance at a block for today at today's diff numbers.
no hard work and with the s-3 load balanced it still earns money with btcguild