You do not "need" anything - whether you might desire to know how much current was being drawn at any moment is a different matter, most I would suggest do not, and at the end of the day such unnecccesary extras simply add complications.
The copious wiring on many layout undersides was a direct result of two factors on DC layouts, with 'cab control' connected to multiple switched sections to enable independent operation of locos, and parking locos in isolated sections; and operation of point motors with track supply switched on the live crossing. This was the typical standard to which club exhibition layouts and ambitious private layouts were constructed before DCC conquered the world.... I have seen a lot on underside of layouts, but found no real explanation of what is being used or for what.
I figured that since one forum is UK based the other US based, we are in the middle, I'll get two different points of view. That way I can get a broader knowledge base of what might be best for me.What beats me is why anyone post's the same question on more than one forum.