My personal preference is for dev boards on site that are a (relatively cheap) site store item. That way the people who want them have access to them, and the people who don't can safely ignore them. Having an extra profile tab seems the worst of both worlds, in that it's an unnecessary appendix for the people who don't use it and it might be too little (or too difficult to format, for people like me who are coding-inept) for the people who actually want it.

In the past I've used mine for lists of miscellaneous facts/tropes, short writing pieces, and relationship and timeline trackers (as distinct from a simple owed/incomplete/completed tracker, which can be grafted onto the profile itself). Some people like quotes, moodboards, and playlists as well, but those are less of a priority for me.