We all know what the Shift key allows you to do after you have selected objects in AutoCAD. That's right, it allows you to deselect objects from your selection set before you continue with your command. If you have never tried this before, do it now. This blog is about the benefit of holding down the Ctrl key when selecting segments of a polyline. My example has a rectangle on the left and a multi-segment polyline on the right. Of course we all know a rectangle is a polyline unless you exploded it.
My task is to remove the top line of the rectangle and make sure the remaining object is a polyline. There are a number of ways you could do this. One would be to use the Polyline Edit (pedit) command with the Edit Vertex / Break option. Another would be to explode the rectangle, remove the line and use Polyline Edit to join it back together.
I offer another method. Hold down the Ctrl key while selecting the polyline segment and then execute your favorite command to delete an object. The segment is removed and the remaining segments are still a polyline. By the way, any selection method will work except using a Fence. You can select multiple segments also with the same result. Of course you can cheat and select non-contiguous segments.
This process works a little different on a multi-segment polyline. If you select one or more segments in the figure on the right you may may end up with two polylines. It depends on the draw order of the original polyline and which segments you select for removal. Oh well, you may still have to use the Polyline Edit command to Join them back together
I tried using the Ctrl key with other commands such as Move and Rotate with mixed results. Try the Ctrl key when working with polylines and see what you can discover.