I'm curious about css best practices for images and graphics, and in what context they really matter. I am putting this post in the mobile dev. forum, because I am assuming that this is the context where they matter most, now or in the future, right?

I'm talking about sprites, repeat background image effects, svg/base64, pseudo selectors -techniques I learned, as I build my responsive site using bootstrap and sublime.

Yet there are so many blogs and big, non-responsive pages full of bells and whistles around...I don't have a smartphone as of yet, so I have no feel of the speed and responsiveness of different web sites relative to how they are coded, or to what degree these css image and graphic-related techniques matter.

In what context does using a sprite or background image, or one div or three, for my little module, matter in terms of the user experience, not semantics, however important.

Thanks for any opinions on this.