With leadcore I can place my baits within inches of the exact depth that I mark fish. And I can do it over and over again. Leadcore line is a nylon line with a thin strand of lead running through it. The more line or weight the deeper a lure will run. An alterative to leadcore line is snap weights.
Snap weights consist of a clothespin type device that snaps onto the line.
I am more accustomed to snap weights. Both systems work to take lures into the extreme depths walleye use in the heat of the summer. The best advice I can give is pick one system and learn it, so that you have confidence your baits are in the zone. Leadcore is speed sensitive. In other words if I increase my trolling speed water resistance on the line will cause the line to lift higher in the water column.