When you select a clip in an FCPX timeline by clicking you only move the Skimmer to that frame in the timeline and not the playhead. To get the playhead there as well just hold OPTION when you click and the playhead will jump to that frame.
Now that might not seem entirely useful as so much in FCPX revolves around the Skimmer and not the playhead. But where I find this useful is when I’m wanting to move or shuffle a clip to a specific frame in the timeline. I might find that spot via skimming the Skimmer and when I do find that spot I want to mark it and drag a clip to that frame. I OPTION + click and that parks the playhead there as my reference when I drag a clip. With snapping turned on it’s a quick way to shuffle around a clip. And since FCPX doesn’t use traditional IN and OUT points I find moving the playhead a much more reliable way to mark a spot for a quick move than a Range Selection Start.
Watch the video below and keep an eye on the playhead and how it moves when OPTION is held. When clicking in the gray area (not on a clip) the playhead will jump. But when clicking a clip the playhead does not jump until you hit the OPTION button.