I've helped a few folks "clean up" their cad drawing for use with a CNC machine. I'm sure folks who are professional drafts-persons or learned Autocad at a school or other professional organization learn most of these things, but a lot of CNC folks here are self taught and learned Autocad by trial and error. Duplicate lines etc, can be hard to locate and select. They tend to increase your file size and cause lots of issues when you try to run the part with a CNC machine. I've been surprised that many folks aren't familiar with the "overkill" command in Autocad. Give it a try! The default settings work well for most issues and will quickly clean up your drawings. In older versions the command was part of the Express Tools... in later versions it's located in the home tab/modify panel, or you can just type it in.