This move is used in unorthodox female wrestling, like erotica or unofficial wrestling competition. It is very hard to escape from, especially if the person initiating the move is heavier than the girl underneath and has good balance. It is also very nice to watch.
The manuever is common between two women who get into a fight. Often the winner will emerge victorious by sitting on top of the defeated loser. It is also used in mixed wrestling where the woman pins the man by sitting on him.