Why play for pennies??

[bdawg31]

I don't mean this to be rude - but can someone please tell me the appeal for playing for pennies online? I read in threads about $.20 winning sessions - i just don't get it. Why not just play for play money? Is there a difference in the games when playing for play money and playing $.01/$.02? Oh, and I have to know, at what point do you 'cash out'?