The "shared" is simply stating that the unit structure is globally shared and can safely be used for multiplayer (i.e., a unit at a specified index will be the same for all clients). Something that is not shared (e.g., screen position) can have different values for each client (e.g., different screen positions).

Are you suggesting we run an AI script from detecting a local address value? Because that will desync the player (because it is a global action). Same with using the Order action.

This condition is pointless.

Even if the first trigger didn't desync the players immediately, this value you're checking here would be desynchronized (because it only changed on one client locally), which would also cause the player to desync when you try using any global action.