If you control the Usenet servers then you control what gets synchronized to your servers. If you filter out the binary groups they will never traverse your network connections to your servers.
You agreed with your peering partners what to send.
I run a text-only Usenet server. As a sibling commenter says, you work out with your peers what you want to receive. I carry most of the text newsgroups, and according to my daily report I got about 3000 new messages yesterday totaling a bit over 9 MB.