Make Image Fully Visible in Workspace

In Lightroom CC and I often end up in situations where the image is off the edge of the workspace especially when I click when the mouse cursor is a magnifying glass with a "+" in it.  Is there a quick way (e.g. keyboard shortcut) to make the image as large as possible and fit it perfectly in the current workspace size?

In general I don't understand what the magnifying glass with "+"  cursor is supposed to do.  It makes no sense to me.  For example the first time it's clicked it makes the image larger (although it may be partly off the edge of the workspace) .  Then dragging side to side does zooming but after the first zoom action, the next time the mouse is pressed the cursor become a "hand" to move the image and never returns to side to side motion doing a zoom until you click again which may again position the image partly off the screen.

Note that I normally work on a Macbook and use pinch to zoom but I seem to spend a lot of time keeping the image as large and possible and fully vislble.

Where is documention on all of this?  i.e. options for positioning and zooming the image in the workspace.