The biggest problem with documentation
that I found on our boat recently was that everything that was installed aftermarket had a separate inline fuse and the instructions said to attach directly to the battery
for best results. Unfortunately the person that installed a lot of the stuff took it to heart and did it exactly as it was diagramed in the instructions. I had fuses
scattered out all over the place in small compartments and wires running from everywhere to the battery
instead of a main or satellite
I think some boat builders could do a better job of preparing larger cruising boats for aftermarket add-ons as well by leaving more room in the fuse blocks and having secondary buses in strategic locations (like the nav station) that can be tapped for power that are fuse or breaker protected and meet all the ABYC requirements instead of bringing everything back to a single
panel or the battery compartment. Then they can be labeled or documented in a manual with where the power is coming from and what the maximum add-on can pull for the wire size, etc.
This may be happening now in the newer boats but it certainly was not priority on any of the older boats I have worked on.
You do get to know your boat very well by tracing those wires all around though.