@plixel@Rodeo generally I setup "horizontal" signal connections inside nodes' _ready() methods, to minimize get_node() calls.
But really, do whatever works for what you're trying to accomplish. There are too many different ways to accomplish the same "thing" for there to be a real 'recommended use' for signals. Technically you don't even need them, you can always grab a node and call one of its methods. It's just that in some cases, it's easier to manage as a signal (especially if you prefer to do things via the Godot editor UI over writing code).