I've got two answers for this one: It can be used to filter multiple carboys in one setting, but I wouldn't hold onto the filter over time and try using it days or weeks apart. As soon as it gets wine on it it becomes a breeding ground for anything it is exposed to.
I agree wholeheartedly with AZMDTed's response. When doing multiple carboys, my practice is to use the filtration media for the whole filtration event. Once finished, toss the media and start with fresh stuff next time around........