This is a good thing to do for multiple reasons:
- You have a new revenue stream born of existing efforts.
- You gain an audience related to your fiction works, also born of said efforts.
- When someone comes to adapt your fiction, you have a document ready to go for them to conform to.
- You have a guideline for fan works to follow, promoting fan engagement.
Speculative fiction routinely deals in world-building, which is where the development of a setting bible becomes well worth the time invested in its creation. By properly preparing it as an encyclopedia-style manuscript and publishing it after the fiction works, you engage the very same processes by which series-based fiction revitalizes entire IPs without having to crank out yet another installment.
If your work becomes attractive enough to get a license, then having a bible handy makes your end easier because you can add their reliance upon it as part of the contract. It gives the artists you've worked with another chance to get their names out there (and thereby build their audience, brand, and business). It gives fans something concrete for their speculations. By publishing it, you get legitimate revenue via the Collectable Item route that Special Editions and Limited/Signed Copies do.
Otherwise, at the very least make your own damned wiki for it and run it yourself. There will be a wiki if you do your part right. Might as well be one you own and control.