This is tangentially related to the question "Social Media Icons - show all visible, or group under 'share'?".
In my organization, we've generally found that displaying the individual icons for Facebook, Twitter, etc. leads to better sharing results on those platforms than showing an "all-in-one" share button...
However, I've also heard the argument that having these icons visible on one's content "reminds" visitors to share on those services (and, thus, increases the overall number of "shares") even if the user doesn't actual sharing service that you've provided. Said another way, the theory goes that because the user saw the Facebook or Twitter icon, they are more likely to independently share the content.
Our (somewhat limited) testing seems to bear this out, but are there accepted research findings or A/B test reports that support this hypothesis?