"ohhhh what does this button do?~~?" hehe van bexer laboritory ^^

well what does it do?
i have been away a year and now im back in full force, but i wonder what is the use of the button?
all i can see is that the reviewed cards end up in the same stack regardless if i click easy or yes.

probaly a n00b question, but i checked the archive and searched the forums with no result