Printing isn't central to the functionality of the package, so cups shouldn't be a requirement.
Version: xpra v2.1.3-r17247 Platform: debian
cups is not required, it is in the "Recommends" section and not the "Depends" section, see browser/xpra/trunk/debian/control. To skip installing recommends, please refer to your package manager's manual.
You're right. For some reason, debian's 'apt-get' dialog listed three groups of packages: those to be installed, those recommended, and those suggested. cups did appear in the list of "to be installed", and since there appeared two other separate lists, for recommended and for suggested, I mistakenly thought cups was 'required'. However, I was able to use the same 'apt-get' to remove cups without it removing xpra. Sorry for the bother.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1696