"i should add that slowplaying has slightly more merit in online tournaments because most of them are very shallow stacked so it's often not hard to get all the chips in even if you miss a street of value. however in cash games, when the stacks are 100 big blinds +, slowplaying is much worse. the times where you win more chips (like a stack) by fastplaying more than makes up for the times you collect one extra bet by slowplaying -- and this is still often the case in tournaments"
But how could fastplaying win a stack but slowplaying can't? What if you make a full house on the turn and he has the nut flush draw. If you make a big bet on the turn he should fold since it would be the mathematically correct play. But if you check and try to let him make a flush you could win his stack if he hits his flush. Remember this is no limit so even if the pot is small going to the turn or to the river doesn't mean you can't win a decent sized pot. The pot might be $1 going to the river, he makes his nut flush. You bet $1, he raises to $5, you reraise to $15, he calls, and you win a decent sized pot. I think what you're talking about is a situation like this...If you have QQ and the flop comes Q 8 7 with a str8 draw and flush draw8, and he has 88. You are thinking that if you fastplay it will get him to reraise and you can get all your money in on the flop, but if you slowplay a flush or straight card might come so you won't be able to get him to go all in since he'll think his trip 8s won't be good. These situations don't really happen that often but when they do come up, yeah it's better to fastplay. Even if you didn't know your opponent had 88 you shouldn't slowplay the nuts here since there's so many draws.