Hence the name. Cancels for binary messages posted to a non-binary newsgroup. Richard Depew, a system administrator, introduced and runs the major bincancel bot. Other people run bincancelling in the newsgroups they hang out on. Bincancelling is also done by moderators of particular newsgroups.
Binaries take up disproportionate amounts of bandwidth.
Although many sites have fast feeds and plenty of memory, many sites have neither. For those smaller sites, binaries present serious load problems. Administrators for such sites may be forced to drop the group altogether rather than damage the rest of their feed. By aliasing out the bincancel pseudosite. If you are not a system administrator, your admin might do this at your request.