Are there any disadvantages to starting blender with the --enable-new-depsgraph argument? The question says it all :). I'm asking because it solved the latency problem between parents and children in the viewport and I will use this as the default blender starting argument (blender --enable-new-depsgraph).
You can watch and track any Dependency graph bugs here:

developer.blender.org > Dependency graph

All of the tickets look resolved now. There are no disadvantages that I know of.

However you never know if somewhere is a bug or not before you test it. If you work in a production environment you probably already test everything before you use it. If your tests are fine I would use --enable-new-depsgraph with ease in mind.