I am new to all of this but the way I understand it is that when you break the borders of the histogram on the right you are clipping your highlights leaving certain highlights in the photo over exposed therefore you are losing some data. When the shadows on the left are beyond the border you are clipping and underexposing causing some detail to be lost in your darkest points.
The ideal image is where both the shadows and highlights are within the borders leading to proper exposure. It does however depend on the image at hand. Some images it can be really hard to prevent all clipping when having good exposure ie. if you took a picture of a boat and the sun reflects off a chrome railing odds are that is going to clip no matter what you do.
Hope this helps a little bit.
The general idea is when you clip out of the borders of the histogram you are losing detail.
With the filmic module I found that yes as you make adjustments you do need to go back to the other sliders to keep everything balanced.