We've made some changes to the way the "play from here" button works in SlideShow 10.
In the timeline, there is a new function, the Play head. With this you can control playability of a video or image. The main difference is that before you could only start at the beginning of an object, i.e you would always see the transition and then the full image or video. With the use of the playhead you can now start at any point within an object, beginning, middle, or end.
For further details and a side by side comparison of how the button worked in SlideShow 9 vs in SlideShow 10 check out this video.