When a text field should have Clear button?

I'm talking about little cross appearing inside text field after typing a text, espessially for search fields in desktop interfaces. But any considerations about general text fields on any platforms are also appreciated.

Some sites use clear button but others don't. I wonder what are pros and cons of both versions?

Example sites with clear button in search field:

  • apple.com/search
  • yahoo.com (on search results page)
  • pinterest.com
  • asos.com
  • translate.google.com

And without:

  • google.com
  • youtube.com
  • stackexchange.com
  • github.com
  • twitter.com