I use the traveled and free capacity graphs together.

If a line has balance, that is probably a good sign.

If a line has higher traveled, it is well-utilized.

If a line has higher free capacity, it may have excess capacity.

If a line has negative free capacity, it is overcrowded.

I evaluate these observations vs profitability. A line with high free capacity versus traveled that is losing money is a line that needs some combination of reduced vehicles, longer waits, or re-routing.