Starting out as a healer, I developed a distaste for the default UI quickly(yes I leveled heals, before LFD too). Grid could be configured to display the information I needed as a healer in a much more configurable and useful manor. Granted the new raid UI is greatly improved. Problem now is that its a comfort thing, i am so used to an altered UI that I cant work with out it, and explaining to your guild that people are dying because you changed your UI and you're not comfortable with it yet doesn't go over well.