The only things I can think of: - they get some data on how many (and what) LAN devices you have - they face fewer support calls from people using DOCSIS mode

The only things I can think of: - they get some data on how many (and what) LAN devices you have - they face fewer support calls from people using DOCSIS modems with one of the buggy intel chipsets, and from people with a random router/modem combination that their support people aren't trained to debug - they can expand their wifi hotspot network (the xfinity wifi hotspot is enabled by default, but the user can turn it off)