With a single size/position KF selected I opened Edit effects curve...
https://dl.dropboxusercontent.com/u/4019461/MEP2014-EditCurve-01.jpg
When I click either of these arrows, both KFs move. I assume therfore that this feature is always meant to be applied to all the KFs?
I'd thought maybe I 'd use it to move a KF precisely one second later, but looks as if I cannot do so.