Have you ever noticed the Drag field at the top of the arrange window?  If the name doesn’t give it away, this option set what happens when you drag a region.  More specifically it determines what happens when you release the region after dragging.

The Shuffle L mode will cause the beginning of a dragged region to snap directly against the end of the region immediately to the left on the same track.  This drag mode is very handy when editing where you will be removing portions of the original audio file.  When you delete a section of audio, all of the regions that follow will shuffle left and snap against the end of any regions that preceded the deleted region.  Assuming your edits were good, you should have seamless playback across the edit point without having to drag or align any regions.