The Snap tool turns snapping on and off. With snapping turned on, layers will automatically 'snap' to other layers and timeline elements so that you can precisely align multiple items.
When snapping is turned on your layers will snap to other items on the timeline when you move or trim them.
Valid snapping targets are:
|•||In and out points of any layer.|
|•||The in and out points of the work area.|
Note that layers do not have to be visible in the track view to be valid snapping targets.
The Slice tool will also snap to edit points, which makes it easy to slice a layer at a specific frame. You can either move the playhead to the correct location before using the Slice tool, or align the slice with a layer on another track.
RECAP Snap is useful for aligning layers and ensuring that there are no unintended gaps in your composite shot. If you need frame-accurate precision, turn snapping off.