For the record, copying the answer from Discord:

We were using USD-based grooms before in all apps including C4D. There were some issues with that format and we switched to a much more lightweight one (YAML). There are also many improvements in terms of what a groom can contain. One of uses for this is being able to export a groom from Maya/Max/UE to C4D while preserving all operators, their paramters, and even referenced meshes and hair. Another use is the new boxing and unboxing functionality which allows collapsing multiple modifiers into a single one.

Ivan Kolev (Software Developer, EPHERE Inc.)

E-mail: ivan.kolev at ephere dot com

Discord: ikolev