So a wiki I'm the admin of got an influx of a number of users whose ratio edit to discussion post is very skewed. They typically have around 10 (usually minor) edits and more than 100 discussion posts, which is because they use they're presumably in that wiki to talk and roleplay with others. While they are not vandals and make no use of the mainspace, they make no constructive edits either. Should I let them be or tell them to roleplay somewhere else? Until now I've let them be, but it can get on my nerves now and then although they aren't doing any harm but they're not improving the mainspace either.
It depends on the purpose of the wiki. However, as a general rule, I would say, if they aren't doing any harm, then leave them be. Of course, "harm" is subjective and potentially relative to the purpose of the wiki. So there isn't an objective criteria that can be applied across all wikis.