We use copper on lake michigan when fishing deep usually. Same concept as leadcore (weighted line to take lures down to depths they normally wouldnt achieve). Unlike leadcore, copper does not have a “sheath” of dacron around it. Therefore, different knots are used to attach it. Reasons for using it are that it achieves greater depth per foot than traditional leadcore and it has a different “fall” rate which gives lure a different look than they would with leadcore. IMO tho, copper is a PITA because of its diameter and memory. If you let it out too quickly, you can create some amazing birdnests. With the release of the new 832 leadcore, I find very little use for copper anymore because Im achieving close to the same depths with the 832. And the 832 is much more user friendly. That being said, Im going to keep my copper setups as there are some days, that for whatever reason, copper is hard to beat. Not sure how practical or helpful it would be on smaller lakes or rivers, but I guess you never know until you try……