The Anchor Point tool, sometimes called the Pan Behind tool in the toolbar, moves the Anchor Point around the layer without changing the position so that you can change the center of the scale and rotation properties. Notice the Position change as you move the Anchor Point. This makes it far easier to move the transition point around the layer so you can get a layer to scale from the left edge instead of the center of the layer or rotate a 3D layer from the left edge to simulate a page turn.
If you change the Anchor Point in the timeline, the Position property does not change, so the layer moves. This also makes sense and sometimes is an efficient workflow. If you want to move a layer around in the Composition panel, use the selection tool (v). If you want to change the location of the Anchor Point without changing the layer Position, use the Anchor Print tool (y). If you change the Position or the Anchor Point tool in the timeline, the layer's position will change in the Composition frame. I use the timeline when I need to use math to precisely adjust the Position or the Anchor Point. If I need to change the center of rotation or scale, the most efficient workflow is usually to use the Anchor Point tool to move it around. If you turn Snapping on, the Anchor Point will snap to the center of an edge, the center of the layer, or the corners.
I hope this helps.