make sketch from selected feature

I am not knew to creating parts and assemblies, but I am somewhat new to making drawings, at least more than just plopping down my views and hitting print.

I made a sketch that had areas I did not want to show in a drawing and found I could only hide or delete entire sketches, not lines within the sketch. I decided to use the "make a sketch from selected feature" and then turned the selected segments for construction, thinking I was a genius and my new sketch would be well defined and coincident with my construction lines.

It is not. It didn't even keep the relations with the lines. Like if I had a square, I now have 4 independent lines other than sharing corners. What's more, it gets rid of overlapping lines, so if I want to keep two adjacent shapes as selectable contours I have to separate and delete segments, connect the open segment to itself and make them collinear again.

The issue arose because I realized I need to show sections of a part in certain drawings but not others. Is there a quick and dirty way to do this, or do I have to basically trace everything again?

Also, even if deleting individual lines in a drawing is possible, it is not a viable option in this situation.

And what is the point of the "create a sketch from selected" feature if it does not keep relations?

SolidworksDrawings And Detailing