Creating a Weldment frame, a layout for a lofted feature or surface, or ANYthing that needs a 3D Sketch ??
Want to create that 3D Sketch in the EASIEST way, EVER ?!
Just make an EXTRUSION of the shape you need, then start a new 3D Sketch. Turn on your EDGE filter !! (“e” key for most people), and WINDOW SELECT the entire part, and CONVERT ENTITIES !!
(you may want to go to Wireframe mode before window selecting, depending on your settings for TOOLS-OPTIONS-SYSTEM OPTIONS-DISPLAY/SELECTION-Selection of Hidden Edges)
You could THEN just HIDE the solid, or do a DELETE BODY on it.
Think how much easier this is to EDIT for changes !!
You can of course get A LOT more complicated than my example with multiple extrudes, extrudes up to surfaces, trimming with planes or surfaces first, etc….
Have FUN !!