That's a purely client-side latency compensation technique; "LC" does nothing more than desynchronize clients, no different to the blatently useless Diablo II "TMC".
You don't know what you're talking about.
Listchecker is what a custom game host uses to host the game. It is not a client-side program; it's only used on the server by the person hosting the game. Nobody else runs listchecker except for the host. It sends updates to clients at a faster pace so the game responds to user actions more quickly. It basically ups the update rate of the server. EDIT: LC isn't actually upping the update rate; hosting the game as a LAN game is what does that. LC just sends the packets to the proper people over the internet using a different port from the game's port so that the game thinks it's a LAN game.
You can test it out for yourself very easily. All you have to do is play a game hosted with LC and without, and it's very evident that the LC game responds to your actions more quickly.
LC games are actually created as LAN games, but LC routes the game packets to the individual clients.
EDIT 2: To be exact, LC hosted games send out updates every 100ms. Normal custom games send out updates every 250ms.