CH is a post-import process which makes routing faster.
You can enable this when you add the profile to profiles_ch in the config.yml
To make CH work in GraphHopper an additional shortcut storage and logic is implemented.
A prepared graph can also be used for normal graph traversal IF you use chGraph.getBaseGraph().
Details about the edge-based version of CH, that also allows taking into account turn costs and restrictions can be found here.