Maybe on a PC, let's say I read some artcile through HN on my phone and want to share it, then a sharing icon can come in handy (because copying and pasting on smartphones is a bit more tedious than just clicking an icon and choosing a service).
But wouldn't something like a share button in that case be something better suited to the browser rather than links on whatever page you are visiting, at the very least? And even then it should be for whatever service I actually use.
