In
theory, fan service is supposed to reward
loyal fans for watching the show by giving them
panty shots,
toplessness that may lack
detail, and
suggestive poses. However, the example already noted regarding
Evangelion disproves this, because if it was a real
gift to the fans,
Misato would not
warn us ahead of time that there would be fan service in the next episode.
Then again, I'm not aware of any other examples of the fan service warning, so maybe it's just that one show.