I believe it's really not necessary, as said above by others, it doesn't add much if anything at all to characters and to the story (unless the story is based on sex jokes).
It is irritating because at this point I cannot watch anime in front of my parents peacefully, if I have doubts that it might include fan service. When it's supposed to be a story with a reasonably good meaning and it slaps you in the face with something like it, I want to pull my hair. How it should be:
-Anime supposed to be serious -> no fan service
-Joke anime supposed to be for 'anyone' -> all the fan service you want
To add more, the fan service should not be included in the main anime in the first place, in my opinion. It should be left as an extra episode or something like that.