Bridge or boat, or some other situation the the current is flowing AWAY from me - fishfinder.
Beach or bay with no "current", just wave action, or littoral current, a high low rig, or same set up with only one hook.....not sure if you'd call that a "hi" or a "lo"....
I do not use fishfinder's on the beach, as it causes some what of a helicoptering of the chunk on the cast. Either that, or the bait goes one direction, the lead the other, and your cast is considerably shortened. And the plastic sleeve rarely sits correctly on the bottom without a line twist around it, so often it does not perform it's intended function anyway. The hi-lo rig is more streamlined and aerodynamic, with the chunk following the lead in a straight line.
I will use the fishfinder on a bridge or a boat, as usually there it's just a lob cast or dropping straight down, and the current moving away from you allows the fishfinder to perform correctly.