What is usefulness and importance of user stylesheet?

Question

I know the importance of Browser styles-sheet and author style-sheet. but what is the importance of user style-sheet?

Why user stylesheet needed?

Does every browser has user style sheet desktop or mobile?

Which type of users use user style sheet and why? I never found anyone who use userstylesheet?

Is thery anything to do for userstyle sheet for XHTML css developer?

Is userstyle sheet related to accessibility?

Why css reset only override on browser css why not on user css?

When we make website , should we consider anything related to user stylesheet?

Answer 1

Why user stylesheet needed?

Because many authors are idiots and many users have special requirement

Does every browser has user styleshhet desktop or mobile?

No

Which type of users use user stylesheet and why?

Ones who need or want to override author CSS or browser defaults

Is thery anything to do for userstyle sheet for XHTML css developer?

Writing sane markup, being consistent, paying attention to the CSS validator's warning about failing to set background colours and foreground colours together.

Is userstyle sheet related to accessibility?

It can be

Why css reset only override on browser css why not on user css?

http://www.w3.org/TR/CSS21/cascade.html#cascade