The switch user function is actually very useful. My wife and I share the home computer and both use Evolution for email. All of my accounts are on my login account and my wife's are on her login account.
Before discovering switch user, she had to close down all of my open programs, and logout and then back in so she could check her email. I would then have to do the same to get back to my programs.
Now we can both login without affecting each other (apart from no sound on the second logged in user???).
If you don't want the option, why not just remove it from K Menu, with the menu editor?