Now that Photoshop CC has an option of extracting assets, should we abandon using slices to export assets to be used by UI developers?
Slices were a necessary tool a decade or more ago, when most sites were built using tables. Photoshop's Save for Web will save slices with HTML. The code uses table, tr and td tags.
Since at least CSS2/XHTML, and emphatically since CSS3 and HTML5 gelled more than a year ago, slices tend to be more of a liability than an asset for anything other than building emails (which still use tables because the CSS support in email readers is so primitive).
They're a possible liability because developers might end up using them as images where they should be using CSS. And in almost all circumstances they're just not useful in modern site design.