This question asking for use cases of a particular command is practically guaranteed to generate a list of answers, many of which will themselves be lists, and most of which will be equally valid. Should it be closed? It's still semi-on-topic, being about a traditional Unix command, so maybe it could be a community wiki instead. What's the policy on such questions?
Community wiki is not an excuse to post a bad question. (It used to be back when Stack Overflow started, but this is no longer the case.) Either your question calls for answers, and it doesn't need CW, or it calls for items or is otherwise inappropriate, in which case the question should not be open at all. See The Future of Community Wiki on the Stack Exchange blog.
This particular question is not a very interesting one, but it does illustrate a bit of unix history. There's no reason why it should attract lists of items rather than answers. If there are multiple practical uses for
factor, it's no different from having multiple methods to rename a bunch of files or partition a disk: an ideal answer would mention all of them and compare them; a decent answer provides at least one and explains why it is relevant.
Because there's no incentive to update them, community wiki lists generally turn into an unmaintained wasteland of good intentions.
Therefore, I'd rather see questions closed when they tend towards discussion or list making. Or better yet if possible, edited to focus the answers. (I'm going to take a stab at this one momentarily.)